From a29c7d37dbc92e358000d1ae19b9d8c148757b3d Mon Sep 17 00:00:00 2001
From: Matthew Phillips <matthew@matthewphillips.info>
Date: Sun, 8 Mar 2026 17:25:33 -0400
Subject: [PATCH 1/6] Replace manual anomalies with a hampel filter

---
 app/components/Package/TrendsChart.vue        |  70 +-----
 .../Package/WeeklyDownloadStats.vue           |   8 +-
 app/utils/download-anomalies.data.ts          |  30 ---
 app/utils/download-anomalies.ts               | 181 ++++++---------
 .../unit/app/utils/download-anomalies.spec.ts | 211 +++++-------------
 5 files changed, 135 insertions(+), 365 deletions(-)
 delete mode 100644 app/utils/download-anomalies.data.ts

diff --git a/app/components/Package/TrendsChart.vue b/app/components/Package/TrendsChart.vue
index 7d08014719..cee8fae8e6 100644
--- a/app/components/Package/TrendsChart.vue
+++ b/app/components/Package/TrendsChart.vue
@@ -23,7 +23,7 @@ import {
   endDateOnlyToUtcMs,
   DEFAULT_PREDICTION_POINTS,
 } from '~/utils/chart-data-prediction'
-import { applyBlocklistCorrection, getAnomaliesForPackages } from '~/utils/download-anomalies'
+import { applyHampelCorrection } from '~/utils/download-anomalies'
 import { copyAltTextForTrendLineChart, sanitise, loadFile, applyEllipsis } from '~/utils/charts'
 
 import('vue-data-ui/style.css')
@@ -978,11 +978,7 @@ const effectiveDataSingle = computed<EvolutionData>(() => {
   if (isDownloadsMetric.value && data.length) {
     const pkg = effectivePackageNames.value[0] ?? props.packageName ?? ''
     if (settings.value.chartFilter.anomaliesFixed) {
-      data = applyBlocklistCorrection({
-        data,
-        packageName: pkg,
-        granularity: displayedGranularity.value,
-      })
+      data = applyHampelCorrection(data)
     }
   }
 
@@ -1026,7 +1022,7 @@ const chartData = computed<{
     let data = state.evolutionsByPackage[pkg] ?? []
     if (isDownloadsMetric.value && data.length) {
       if (settings.value.chartFilter.anomaliesFixed) {
-        data = applyBlocklistCorrection({ data, packageName: pkg, granularity })
+        data = applyHampelCorrection(data)
       }
     }
     const points = extractSeriesPoints(granularity, data)
@@ -1556,20 +1552,6 @@ const chartConfig = computed<VueUiXyConfig>(() => {
 const isDownloadsMetric = computed(() => selectedMetric.value === 'downloads')
 const showCorrectionControls = shallowRef(false)
 
-const packageAnomalies = computed(() => getAnomaliesForPackages(effectivePackageNames.value))
-const hasAnomalies = computed(() => packageAnomalies.value.length > 0)
-
-function formatAnomalyDate(dateStr: string) {
-  const [y, m, d] = dateStr.split('-').map(Number)
-  if (!y || !m || !d) return dateStr
-  return new Intl.DateTimeFormat(locale.value, {
-    year: 'numeric',
-    month: 'short',
-    day: 'numeric',
-    timeZone: 'UTC',
-  }).format(new Date(Date.UTC(y, m - 1, d)))
-}
-
 // Trigger data loading when the metric is switched
 watch(selectedMetric, value => {
   if (!isMounted.value) return
@@ -1722,64 +1704,28 @@ watch(selectedMetric, value => {
               class="text-2xs font-mono text-fg-subtle tracking-wide uppercase flex items-center justify-between"
             >
               {{ $t('package.trends.known_anomalies') }}
-              <TooltipApp interactive :to="inModal ? '#chart-modal' : undefined">
+              <TooltipApp :to="inModal ? '#chart-modal' : undefined">
                 <button
                   type="button"
                   class="i-lucide:info w-3.5 h-3.5 text-fg-muted cursor-help"
                   :aria-label="$t('package.trends.known_anomalies')"
                 />
                 <template #content>
-                  <div class="flex flex-col gap-3">
-                    <p class="text-xs text-fg-muted">
-                      {{ $t('package.trends.known_anomalies_description') }}
-                    </p>
-                    <div v-if="hasAnomalies">
-                      <p class="text-xs text-fg-subtle font-medium">
-                        {{ $t('package.trends.known_anomalies_ranges') }}
-                      </p>
-                      <ul class="text-xs text-fg-subtle list-disc list-inside">
-                        <li v-for="a in packageAnomalies" :key="`${a.packageName}-${a.start}`">
-                          {{
-                            isMultiPackageMode
-                              ? $t('package.trends.known_anomalies_range_named', {
-                                  packageName: a.packageName,
-                                  start: formatAnomalyDate(a.start),
-                                  end: formatAnomalyDate(a.end),
-                                })
-                              : $t('package.trends.known_anomalies_range', {
-                                  start: formatAnomalyDate(a.start),
-                                  end: formatAnomalyDate(a.end),
-                                })
-                          }}
-                        </li>
-                      </ul>
-                    </div>
-                    <p v-else class="text-xs text-fg-muted">
-                      {{ $t('package.trends.known_anomalies_none', effectivePackageNames.length) }}
-                    </p>
-                    <div class="flex justify-end">
-                      <LinkBase
-                        to="https://github.com/npmx-dev/npmx.dev/edit/main/app/utils/download-anomalies.data.ts"
-                        class="text-xs text-accent"
-                      >
-                        {{ $t('package.trends.known_anomalies_contribute') }}
-                      </LinkBase>
-                    </div>
-                  </div>
+                  <p class="text-xs text-fg-muted">
+                    {{ $t('package.trends.known_anomalies_description') }}
+                  </p>
                 </template>
               </TooltipApp>
             </span>
             <label
               class="flex items-center gap-1.5 text-2xs font-mono text-fg-subtle cursor-pointer h-4"
-              :class="{ 'opacity-50 pointer-events-none': !hasAnomalies }"
             >
               <input
-                :checked="settings.chartFilter.anomaliesFixed && hasAnomalies"
+                :checked="settings.chartFilter.anomaliesFixed"
                 @change="
                   settings.chartFilter.anomaliesFixed = ($event.target as HTMLInputElement).checked
                 "
                 type="checkbox"
-                :disabled="!hasAnomalies"
                 class="accent-[var(--accent-color,var(--fg-subtle))]"
               />
               {{ $t('package.trends.apply_correction') }}
diff --git a/app/components/Package/WeeklyDownloadStats.vue b/app/components/Package/WeeklyDownloadStats.vue
index c0a0957e34..9d636259d1 100644
--- a/app/components/Package/WeeklyDownloadStats.vue
+++ b/app/components/Package/WeeklyDownloadStats.vue
@@ -4,7 +4,7 @@ import { useCssVariables } from '~/composables/useColors'
 import type { WeeklyDataPoint } from '~/types/chart'
 import { applyDataCorrection } from '~/utils/chart-data-correction'
 import { OKLCH_NEUTRAL_FALLBACK, lightenOklch } from '~/utils/colors'
-import { applyBlocklistCorrection } from '~/utils/download-anomalies'
+import { applyHampelCorrection } from '~/utils/download-anomalies'
 import type { RepoRef } from '#shared/utils/git-providers'
 import type { VueUiSparklineConfig, VueUiSparklineDatasetItem } from 'vue-data-ui'
 import { onKeyDown } from '@vueuse/core'
@@ -186,11 +186,7 @@ const correctedDownloads = computed<WeeklyDataPoint[]>(() => {
   let data = weeklyDownloads.value as WeeklyDataPoint[]
   if (!data.length) return data
   if (settings.value.chartFilter.anomaliesFixed) {
-    data = applyBlocklistCorrection({
-      data,
-      packageName: props.packageName,
-      granularity: 'weekly',
-    }) as WeeklyDataPoint[]
+    data = applyHampelCorrection(data) as WeeklyDataPoint[]
   }
   data = applyDataCorrection(data, settings.value.chartFilter) as WeeklyDataPoint[]
   return data
diff --git a/app/utils/download-anomalies.data.ts b/app/utils/download-anomalies.data.ts
deleted file mode 100644
index 3cb23fb858..0000000000
--- a/app/utils/download-anomalies.data.ts
+++ /dev/null
@@ -1,30 +0,0 @@
-import type { DownloadAnomaly } from './download-anomalies'
-
-export const DOWNLOAD_ANOMALIES: DownloadAnomaly[] = [
-  // vite rogue CI spike
-  {
-    packageName: 'vite',
-    start: { date: '2025-08-04', weeklyDownloads: 33_913_132 },
-    end: { date: '2025-09-08', weeklyDownloads: 38_665_727 },
-  },
-  {
-    packageName: 'svelte',
-    start: { date: '2022-11-15', weeklyDownloads: 75_233 },
-    end: { date: '2022-11-30', weeklyDownloads: 69_524 },
-  },
-  {
-    packageName: 'svelte',
-    start: { date: '2023-06-19', weeklyDownloads: 107_491 },
-    end: { date: '2023-06-22', weeklyDownloads: 112_432 },
-  },
-  {
-    packageName: 'svelte',
-    start: { date: '2023-11-18', weeklyDownloads: 59_611 },
-    end: { date: '2023-11-21', weeklyDownloads: 150_680 },
-  },
-  /**
-   * NOTE:
-   *  - please add new entries above this comment.
-   *  - Add a comment before any new entry to explain the change
-   **/
-]
diff --git a/app/utils/download-anomalies.ts b/app/utils/download-anomalies.ts
index ae2798d0bd..16e8c8ee19 100644
--- a/app/utils/download-anomalies.ts
+++ b/app/utils/download-anomalies.ts
@@ -1,133 +1,90 @@
-import type { ChartTimeGranularity, EvolutionData } from '~/types/chart'
-import { DOWNLOAD_ANOMALIES } from './download-anomalies.data'
+import type { EvolutionData } from '~/types/chart'
 
-export type DownloadAnomalyBound = {
-  date: string // YYYY-MM-DD
-  weeklyDownloads: number
-}
+/**
+ * Hampel filter for automatic anomaly detection and correction.
+ *
+ * For each data point, computes the median and Median Absolute Deviation (MAD)
+ * of a surrounding window. Points deviating more than `threshold` MADs from
+ * the local median are flagged as anomalies and replaced with the median.
+ *
+ * This approach is unbiased — it applies the same statistical test to every
+ * package equally, with no manual curation.
+ */
 
-export type DownloadAnomaly = {
-  packageName: string
-  start: DownloadAnomalyBound
-  end: DownloadAnomalyBound
-}
+const DEFAULT_HALF_WINDOW = 3
+const DEFAULT_THRESHOLD = 3
 
-function getDateString(point: Record<string, any>, granularity: ChartTimeGranularity): string {
-  switch (granularity) {
-    case 'daily':
-      return point.day
-    case 'weekly':
-      return point.weekStart
-    case 'monthly':
-      return `${point.month}-01`
-    case 'yearly':
-      return `${point.year}-01-01`
-  }
+function median(values: number[]): number {
+  const sorted = [...values].sort((a, b) => a - b)
+  const mid = Math.floor(sorted.length / 2)
+  return sorted.length % 2 !== 0 ? sorted[mid]! : (sorted[mid - 1]! + sorted[mid]!) / 2
 }
 
-/**
- * For daily the point date falls strictly between the anomaly bounds.
- * For weekly the point date is the week start, and the full 7-day range is
- * checked so any overlapping week is affected.
- * For monthly/yearly the anomaly bounds are truncated to the same resolution
- * so that any period overlapping the anomaly is caught (inclusive).
- */
-function isDateAffected(
-  date: string,
-  anomaly: DownloadAnomaly,
-  granularity: ChartTimeGranularity,
-): boolean {
-  switch (granularity) {
-    case 'daily':
-      return date > anomaly.start.date && date < anomaly.end.date
-    case 'weekly': {
-      const startWeek = date
-      const weekStartDate = new Date(`${date}T00:00:00Z`)
-      const weekEndDate = new Date(weekStartDate)
-      weekEndDate.setUTCDate(weekEndDate.getUTCDate() + 6)
-      const endWeek = weekEndDate.toISOString().slice(0, 10)
-      return startWeek < anomaly.end.date && endWeek > anomaly.start.date
-    }
-    case 'monthly': {
-      const monthStart = date
-      const monthStartDate = new Date(`${date}T00:00:00Z`)
-      const monthEndDate = new Date(monthStartDate)
-      monthEndDate.setUTCMonth(monthEndDate.getUTCMonth() + 1)
-      monthEndDate.setUTCDate(monthEndDate.getUTCDate() - 1)
-      const monthEnd = monthEndDate.toISOString().slice(0, 10)
-      return monthStart < anomaly.end.date && monthEnd > anomaly.start.date
-    }
-    case 'yearly': {
-      const yearStart = date
-      const yearEnd = `${date.slice(0, 4)}-12-31`
-      return yearStart < anomaly.end.date && yearEnd > anomaly.start.date
-    }
-  }
+function mad(values: number[], med: number): number {
+  const deviations = values.map(v => Math.abs(v - med))
+  return median(deviations)
 }
 
-function scaleWeeklyValue(weeklyValue: number, granularity: ChartTimeGranularity): number {
-  switch (granularity) {
-    case 'daily':
-      return Math.round(weeklyValue / 7)
-    case 'weekly':
-      return weeklyValue
-    case 'monthly':
-      return Math.round((weeklyValue / 7) * 30)
-    case 'yearly':
-      return Math.round((weeklyValue / 7) * 365)
-  }
-}
+export function applyHampelCorrection(
+  data: EvolutionData,
+  opts?: { halfWindow?: number; threshold?: number },
+): EvolutionData {
+  // halfWindow controls how many neighbors on each side to consider.
+  // A window of 3 means we look at 7 points total (3 left + current + 3 right).
+  const halfWindow = opts?.halfWindow ?? DEFAULT_HALF_WINDOW
 
-export function getAnomaliesForPackages(
-  packageNames: string[],
-): { packageName: string; start: string; end: string }[] {
-  return DOWNLOAD_ANOMALIES.filter(a => packageNames.includes(a.packageName)).map(a => ({
-    packageName: a.packageName,
-    start: a.start.date,
-    end: a.end.date,
-  }))
-}
+  // threshold controls sensitivity. A value of 3 means a point must deviate
+  // more than 3 scaled MADs from the local median to be flagged.
+  // Higher = less sensitive, lower = more aggressive filtering.
+  const threshold = opts?.threshold ?? DEFAULT_THRESHOLD
 
-export function applyBlocklistCorrection(opts: {
-  data: EvolutionData
-  packageName: string
-  granularity: ChartTimeGranularity
-}): EvolutionData {
-  const { data, packageName, granularity } = opts
-  const anomalies = DOWNLOAD_ANOMALIES.filter(a => a.packageName === packageName)
-  if (!anomalies.length) return data
+  // Not enough data to form a full window — return as-is.
+  if (data.length < halfWindow * 2 + 1) return data
 
-  // Clone to avoid mutation
+  const values = (data as Array<{ value: number }>).map(d => d.value)
+  // Clone to avoid mutating the original data.
   const result = (data as Array<Record<string, any>>).map(d => ({ ...d }))
 
-  for (const anomaly of anomalies) {
-    // Find indices of affected points
-    const affectedIndices: number[] = []
-    for (let i = 0; i < result.length; i++) {
-      const date = getDateString(result[i]!, granularity)
-      if (isDateAffected(date, anomaly, granularity)) {
-        affectedIndices.push(i)
-      }
-    }
+  for (let i = 0; i < values.length; i++) {
+    // Build a sliding window around the current point, clamped to array bounds.
+    const start = Math.max(0, i - halfWindow)
+    const end = Math.min(values.length - 1, i + halfWindow)
+    const window = values.slice(start, end + 1)
 
-    if (!affectedIndices.length) continue
+    // The median is robust to outliers — unlike the mean, a single spike
+    // won't pull it away from the true central tendency.
+    const windowMedian = median(window)
 
-    const firstAffected = affectedIndices[0]!
-    const lastAffected = affectedIndices[affectedIndices.length - 1]!
+    // MAD (Median Absolute Deviation) measures spread without being
+    // influenced by the outliers we're trying to detect.
+    const windowMad = mad(window, windowMedian)
 
-    // Use neighbors when available, fall back to scaled weeklyDownloads
-    const scaledStart = scaleWeeklyValue(anomaly.start.weeklyDownloads, granularity)
-    const scaledEnd = scaleWeeklyValue(anomaly.end.weeklyDownloads, granularity)
+    // How far this point is from the local median.
+    const deviation = Math.abs(values[i]! - windowMedian)
 
-    const startVal = firstAffected > 0 ? result[firstAffected - 1]!.value : scaledStart
-    const endVal = lastAffected < result.length - 1 ? result[lastAffected + 1]!.value : scaledEnd
+    // MAD of 0 means most values in the window are identical.
+    // If this point differs from the median at all, it's an outlier.
+    if (windowMad === 0) {
+      if (deviation > 0) {
+        result[i]!.value = Math.round(windowMedian)
+        result[i]!.hasAnomaly = true
+      }
+      continue
+    }
 
-    const count = affectedIndices.length
-    for (let i = 0; i < count; i++) {
-      const t = (i + 1) / (count + 1)
-      result[affectedIndices[i]!]!.value = Math.round(startVal + t * (endVal - startVal))
-      result[affectedIndices[i]!]!.hasAnomaly = true
+    // Scale MAD to approximate standard deviation using the consistency
+    // constant 1.4826 (valid for normally distributed data).
+    // The resulting score is essentially "how many standard deviations
+    // away from the local median is this point?"
+    const score = deviation / (windowMad * 1.4826)
+
+    // If the score exceeds the threshold, replace with the median.
+    // This corrects the spike while preserving the surrounding trend.
+    if (score > threshold) {
+      result[i]!.value = Math.round(windowMedian)
+      result[i]!.hasAnomaly = true
     }
   }
+
   return result as EvolutionData
 }
diff --git a/test/unit/app/utils/download-anomalies.spec.ts b/test/unit/app/utils/download-anomalies.spec.ts
index 094e6d44ef..6dd76f29ad 100644
--- a/test/unit/app/utils/download-anomalies.spec.ts
+++ b/test/unit/app/utils/download-anomalies.spec.ts
@@ -1,183 +1,84 @@
 import { describe, expect, it } from 'vitest'
-import { applyBlocklistCorrection } from '../../../../app/utils/download-anomalies'
-import type {
-  MonthlyDataPoint,
-  WeeklyDataPoint,
-  YearlyDataPoint,
-} from '../../../../app/types/chart'
+import { applyHampelCorrection } from '../../../../app/utils/download-anomalies'
+import type { WeeklyDataPoint } from '../../../../app/types/chart'
 
-/** Helper to build a WeeklyDataPoint from a start date and value. */
-function week(weekStart: string, value: number): WeeklyDataPoint {
-  const start = new Date(`${weekStart}T00:00:00Z`)
-  const end = new Date(start)
-  end.setUTCDate(end.getUTCDate() + 6)
-  const weekEnd = end.toISOString().slice(0, 10)
+function makeWeeklyPoint(weekStart: string, value: number): WeeklyDataPoint {
   return {
     value,
-    weekKey: `${weekStart}_${weekEnd}`,
+    weekKey: `${weekStart}_end`,
     weekStart,
-    weekEnd,
-    timestampStart: start.getTime(),
-    timestampEnd: end.getTime(),
+    weekEnd: weekStart,
+    timestampStart: 0,
+    timestampEnd: 0,
   }
 }
 
-function month(monthStr: string, value: number): MonthlyDataPoint {
-  return {
-    value,
-    month: monthStr,
-    timestamp: new Date(`${monthStr}-01T00:00:00Z`).getTime(),
-  }
-}
-
-function year(yearStr: string, value: number): YearlyDataPoint {
-  return {
-    value,
-    year: yearStr,
-    timestamp: new Date(`${yearStr}-01-01T00:00:00Z`).getTime(),
-  }
-}
-
-describe('applyBlocklistCorrection', () => {
-  // Anomaly Nov 2022: start=2022-11-15, end=2022-11-30
-  it('corrects weeks overlapping the anomaly', () => {
-    const data = [
-      week('2022-11-07', 100),
-      week('2022-11-14', 999),
-      week('2022-11-21', 999),
-      week('2022-11-28', 999),
-      week('2022-12-05', 200),
-    ]
-
-    expect(
-      applyBlocklistCorrection({
-        data,
-        packageName: 'svelte',
-        granularity: 'weekly',
-      }),
-    ).toEqual([
-      data[0],
-      { ...data[1], value: 125, hasAnomaly: true },
-      { ...data[2], value: 150, hasAnomaly: true },
-      { ...data[3], value: 175, hasAnomaly: true },
-      data[4],
-    ])
-  })
-
-  // Anomaly Jun 2023: start=2023-06-19, end=2023-06-22
-  it('does not over-correct a week starting on the anomaly end boundary', () => {
-    const data = [
-      week('2023-06-01', 500_000),
-      week('2023-06-08', 500_000),
-      week('2023-06-15', 10_000_000), // contains spike
-      week('2023-06-22', 500_000), // starts on anomaly end boundary — normal!
-      week('2023-06-29', 500_000),
+describe('applyHampelCorrection', () => {
+  it('flags and corrects a spike in the middle of steady data', () => {
+    const data: WeeklyDataPoint[] = [
+      makeWeeklyPoint('2022-11-07', 100),
+      makeWeeklyPoint('2022-11-14', 100),
+      makeWeeklyPoint('2022-11-21', 100),
+      makeWeeklyPoint('2022-11-28', 1000), // spike
+      makeWeeklyPoint('2022-12-05', 100),
+      makeWeeklyPoint('2022-12-12', 100),
+      makeWeeklyPoint('2022-12-19', 100),
     ]
 
-    const result = applyBlocklistCorrection({
-      data,
-      packageName: 'svelte',
-      granularity: 'weekly',
-    }) as WeeklyDataPoint[]
+    const result = applyHampelCorrection(data) as WeeklyDataPoint[]
 
-    // The spike week must be corrected
-    expect(result[2]!.hasAnomaly).toBe(true)
-    expect(result[2]!.value).toBeLessThan(1_000_000)
+    // The spike should be corrected
+    expect(result[3]!.hasAnomaly).toBe(true)
+    expect(result[3]!.value).toBe(100) // replaced with median
 
-    // The boundary week must NOT be modified
-    expect(result[3]!.value).toBe(500_000)
-    expect(result[3]!.hasAnomaly).toBeUndefined()
-  })
-
-  it('does not over-correct a week ending on the anomaly start boundary', () => {
-    const data = [
-      week('2023-06-13', 500_000), // ends on anomaly start boundary — normal!
-      week('2023-06-20', 10_000_000), // contains spike
-      week('2023-06-27', 500_000),
-    ]
-
-    const result = applyBlocklistCorrection({
-      data,
-      packageName: 'svelte',
-      granularity: 'weekly',
-    }) as WeeklyDataPoint[]
-
-    // The boundary week must NOT be modified
-    expect(result[0]!.value).toBe(500_000)
+    // Non-spike points should be unchanged
+    expect(result[0]!.value).toBe(100)
     expect(result[0]!.hasAnomaly).toBeUndefined()
-
-    // The spike week must be corrected
-    expect(result[1]!.hasAnomaly).toBe(true)
-    expect(result[1]!.value).toBeLessThan(1_000_000)
+    expect(result[1]!.value).toBe(100)
+    expect(result[6]!.value).toBe(100)
   })
 
-  // Vite anomaly: start=2025-08-04, end=2025-09-08 (spans Aug-Sep)
-  it('does not over-correct a month that only touches the anomaly end boundary', () => {
-    const data = [
-      month('2025-07', 30_000_000),
-      month('2025-08', 100_000_000), // contains spike
-      month('2025-09', 100_000_000), // contains spike (Sep 1-7)
-      month('2025-10', 30_000_000), // after anomaly end — normal!
+  it('does not flag gradual growth as anomalies', () => {
+    const data: WeeklyDataPoint[] = [
+      makeWeeklyPoint('2022-11-07', 100),
+      makeWeeklyPoint('2022-11-14', 110),
+      makeWeeklyPoint('2022-11-21', 120),
+      makeWeeklyPoint('2022-11-28', 130),
+      makeWeeklyPoint('2022-12-05', 140),
+      makeWeeklyPoint('2022-12-12', 150),
+      makeWeeklyPoint('2022-12-19', 160),
     ]
 
-    const result = applyBlocklistCorrection({
-      data,
-      packageName: 'vite',
-      granularity: 'monthly',
-    }) as MonthlyDataPoint[]
-
-    expect(result[1]!.hasAnomaly).toBe(true)
-    expect(result[2]!.hasAnomaly).toBe(true)
+    const result = applyHampelCorrection(data) as WeeklyDataPoint[]
 
-    // October must NOT be modified
-    expect(result[3]!.value).toBe(30_000_000)
-    expect(result[3]!.hasAnomaly).toBeUndefined()
+    for (const point of result) {
+      expect(point.hasAnomaly).toBeUndefined()
+    }
   })
 
-  it('does not over-correct a month that only touches the anomaly start boundary', () => {
-    const data = [
-      month('2025-07', 30_000_000), // before anomaly start — normal!
-      month('2025-08', 100_000_000), // contains spike
-      month('2025-09', 100_000_000), // contains spike
-      month('2025-10', 30_000_000),
+  it('returns data unchanged when too few points for the window', () => {
+    const data: WeeklyDataPoint[] = [
+      makeWeeklyPoint('2022-11-07', 100),
+      makeWeeklyPoint('2022-11-14', 1000),
+      makeWeeklyPoint('2022-11-21', 100),
     ]
 
-    const result = applyBlocklistCorrection({
-      data,
-      packageName: 'vite',
-      granularity: 'monthly',
-    }) as MonthlyDataPoint[]
-
-    // July must NOT be modified
-    expect(result[0]!.value).toBe(30_000_000)
-    expect(result[0]!.hasAnomaly).toBeUndefined()
-
-    expect(result[1]!.hasAnomaly).toBe(true)
-    expect(result[2]!.hasAnomaly).toBe(true)
+    const result = applyHampelCorrection(data) as WeeklyDataPoint[]
+    expect(result[1]!.value).toBe(1000) // not enough data to detect
   })
 
-  it('does not over-correct a year that only touches the anomaly boundary', () => {
-    const data = [
-      year('2024', 500_000_000),
-      year('2025', 2_000_000_000), // contains spike
-      year('2026', 500_000_000),
+  it('does not mutate the original data', () => {
+    const data: WeeklyDataPoint[] = [
+      makeWeeklyPoint('2022-11-07', 100),
+      makeWeeklyPoint('2022-11-14', 100),
+      makeWeeklyPoint('2022-11-21', 100),
+      makeWeeklyPoint('2022-11-28', 1000),
+      makeWeeklyPoint('2022-12-05', 100),
+      makeWeeklyPoint('2022-12-12', 100),
+      makeWeeklyPoint('2022-12-19', 100),
     ]
 
-    const result = applyBlocklistCorrection({
-      data,
-      packageName: 'vite',
-      granularity: 'yearly',
-    }) as YearlyDataPoint[]
-
-    // 2024 must NOT be modified
-    expect(result[0]!.value).toBe(500_000_000)
-    expect(result[0]!.hasAnomaly).toBeUndefined()
-
-    // 2025 must be corrected
-    expect(result[1]!.hasAnomaly).toBe(true)
-
-    // 2026 must NOT be modified
-    expect(result[2]!.value).toBe(500_000_000)
-    expect(result[2]!.hasAnomaly).toBeUndefined()
+    applyHampelCorrection(data)
+    expect(data[3]!.value).toBe(1000) // original unchanged
   })
 })

From 9cf5d8b7a4d6908430dd9f1a233ddfc30e8eb0a8 Mon Sep 17 00:00:00 2001
From: Matthew Phillips <matthew@matthewphillips.info>
Date: Sun, 8 Mar 2026 17:39:41 -0400
Subject: [PATCH 2/6] Fix typechecking

---
 app/components/Package/TrendsChart.vue | 1 -
 1 file changed, 1 deletion(-)

diff --git a/app/components/Package/TrendsChart.vue b/app/components/Package/TrendsChart.vue
index cee8fae8e6..21fcc010fd 100644
--- a/app/components/Package/TrendsChart.vue
+++ b/app/components/Package/TrendsChart.vue
@@ -976,7 +976,6 @@ const effectiveDataSingle = computed<EvolutionData>(() => {
   }
 
   if (isDownloadsMetric.value && data.length) {
-    const pkg = effectivePackageNames.value[0] ?? props.packageName ?? ''
     if (settings.value.chartFilter.anomaliesFixed) {
       data = applyHampelCorrection(data)
     }

From 55388db86c694fe5e027fbb1fc18694dcdd8af87 Mon Sep 17 00:00:00 2001
From: Matthew Phillips <matthew@matthewphillips.info>
Date: Sun, 8 Mar 2026 17:42:33 -0400
Subject: [PATCH 3/6] Remove i18n keys

---
 i18n/locales/bg-BG.json |  5 -----
 i18n/locales/cs-CZ.json |  5 -----
 i18n/locales/de-DE.json |  5 -----
 i18n/locales/en.json    |  5 -----
 i18n/locales/es.json    |  5 -----
 i18n/locales/fr-FR.json |  5 -----
 i18n/locales/hu-HU.json |  5 -----
 i18n/locales/id-ID.json |  5 -----
 i18n/locales/ja-JP.json |  5 -----
 i18n/locales/pl-PL.json |  5 -----
 i18n/locales/ru-RU.json |  5 -----
 i18n/locales/tr-TR.json |  5 -----
 i18n/locales/uk-UA.json |  5 -----
 i18n/locales/zh-CN.json |  5 -----
 i18n/locales/zh-TW.json |  5 -----
 i18n/schema.json        | 15 ---------------
 16 files changed, 90 deletions(-)

diff --git a/i18n/locales/bg-BG.json b/i18n/locales/bg-BG.json
index c2865f990f..35c1472b30 100644
--- a/i18n/locales/bg-BG.json
+++ b/i18n/locales/bg-BG.json
@@ -421,11 +421,6 @@
       "smoothing": "Изглаждане",
       "known_anomalies": "Известни аномалии",
       "known_anomalies_description": "Интерполира известни скокове в изтеглянията, причинени от ботове или CI проблеми.",
-      "known_anomalies_ranges": "Диапазони на аномалии",
-      "known_anomalies_range": "От {start} до {end}",
-      "known_anomalies_range_named": "{packageName}: от {start} до {end}",
-      "known_anomalies_none": "Няма известни аномалии за този пакет. | Няма известни аномалии за тези пакети.",
-      "known_anomalies_contribute": "Допринесете данни за аномалии",
       "apply_correction": "Прилагане на корекция",
       "copy_alt": {
         "trend_none": "предимно стабилна",
diff --git a/i18n/locales/cs-CZ.json b/i18n/locales/cs-CZ.json
index 59aae4e8d7..c694db7fa4 100644
--- a/i18n/locales/cs-CZ.json
+++ b/i18n/locales/cs-CZ.json
@@ -470,11 +470,6 @@
       "smoothing": "Vyhlazování",
       "known_anomalies": "Známé anomálie",
       "known_anomalies_description": "Interpoluje přes známé špičky stažení způsobené boty nebo problémy s CI.",
-      "known_anomalies_ranges": "Rozsahy anomálií",
-      "known_anomalies_range": "Od {start} do {end}",
-      "known_anomalies_range_named": "{packageName}: od {start} do {end}",
-      "known_anomalies_none": "Žádné známé anomálie pro tento balíček. | Žádné známé anomálie pro tyto balíčky.",
-      "known_anomalies_contribute": "Přispět daty o anomáliích",
       "apply_correction": "Aplikovat korekci",
       "copy_alt": {
         "trend_none": "převážně stabilní",
diff --git a/i18n/locales/de-DE.json b/i18n/locales/de-DE.json
index eb81ebdec8..e506886eb1 100644
--- a/i18n/locales/de-DE.json
+++ b/i18n/locales/de-DE.json
@@ -460,11 +460,6 @@
       "smoothing": "Glättung",
       "known_anomalies": "Bekannte Anomalien",
       "known_anomalies_description": "Gleicht bekannte Download-Ausreißer aus, die durch Bots oder CI-Probleme entstanden sind.",
-      "known_anomalies_ranges": "Anomalie-Zeiträume",
-      "known_anomalies_range": "Von {start} bis {end}",
-      "known_anomalies_range_named": "{packageName}: vom {start} bis zum {end}",
-      "known_anomalies_none": "Keine bekannten Anomalien für dieses Paket. | Keine bekannten Anomalien für diese Pakete.",
-      "known_anomalies_contribute": "Anomalie-Daten einreichen",
       "apply_correction": "Korrektur anwenden",
       "copy_alt": {
         "trend_none": "weitgehend gleichbleibenden",
diff --git a/i18n/locales/en.json b/i18n/locales/en.json
index c187265c73..2c620c970d 100644
--- a/i18n/locales/en.json
+++ b/i18n/locales/en.json
@@ -472,11 +472,6 @@
       "prediction": "Prediction",
       "known_anomalies": "Known anomalies",
       "known_anomalies_description": "Interpolates over known download spikes caused by bots or CI issues.",
-      "known_anomalies_ranges": "Anomaly ranges",
-      "known_anomalies_range": "From {start} to {end}",
-      "known_anomalies_range_named": "{packageName}: from {start} to {end}",
-      "known_anomalies_none": "No known anomalies for this package. | No known anomalies for these packages.",
-      "known_anomalies_contribute": "Contribute anomaly data",
       "apply_correction": "Apply correction",
       "copy_alt": {
         "trend_none": "mostly flat",
diff --git a/i18n/locales/es.json b/i18n/locales/es.json
index 87f719488c..77bef7f7ac 100644
--- a/i18n/locales/es.json
+++ b/i18n/locales/es.json
@@ -421,11 +421,6 @@
       "smoothing": "Suavizado",
       "known_anomalies": "Anomalías conocidas",
       "known_anomalies_description": "Interpola sobre picos de descarga conocidos causados por bots o problemas de CI.",
-      "known_anomalies_ranges": "Rangos de anomalías",
-      "known_anomalies_range": "Desde {start} hasta {end}",
-      "known_anomalies_range_named": "{packageName}: desde {start} hasta {end}",
-      "known_anomalies_none": "No hay anomalías conocidas para este paquete. | No hay anomalías conocidas para estos paquetes.",
-      "known_anomalies_contribute": "Contribuir con datos de anomalías",
       "apply_correction": "Aplicar corrección",
       "copy_alt": {
         "trend_none": "mayormente plano",
diff --git a/i18n/locales/fr-FR.json b/i18n/locales/fr-FR.json
index add6ac7b0b..743526dc5f 100644
--- a/i18n/locales/fr-FR.json
+++ b/i18n/locales/fr-FR.json
@@ -460,11 +460,6 @@
       "smoothing": "Lissage",
       "known_anomalies": "Anomalies connues",
       "known_anomalies_description": "Interpole les pics de téléchargements connus causés par des bots ou des problèmes de CI.",
-      "known_anomalies_ranges": "Plages d'anomalies",
-      "known_anomalies_range": "Du {start} au {end}",
-      "known_anomalies_range_named": "{packageName} : du {start} au {end}",
-      "known_anomalies_none": "Aucune anomalie connue pour ce paquet. | Aucune anomalie connue pour ces paquets.",
-      "known_anomalies_contribute": "Contribuer des données d'anomalie",
       "apply_correction": "Appliquer la correction",
       "copy_alt": {
         "trend_none": "globalement stable",
diff --git a/i18n/locales/hu-HU.json b/i18n/locales/hu-HU.json
index 87b645f334..63bc587eda 100644
--- a/i18n/locales/hu-HU.json
+++ b/i18n/locales/hu-HU.json
@@ -421,11 +421,6 @@
       "smoothing": "Simítás",
       "known_anomalies": "Ismert anomáliák",
       "known_anomalies_description": "Interpolálja a botok vagy CI-problémák által okozott ismert letöltési csúcsokat.",
-      "known_anomalies_ranges": "Anomália tartományok",
-      "known_anomalies_range": "Innen: {start} eddig: {end}",
-      "known_anomalies_range_named": "{packageName}: innen: {start} eddig: {end}",
-      "known_anomalies_none": "Nincs ismert anomália erre a csomagra. | Nincs ismert anomália ezekre a csomagokra.",
-      "known_anomalies_contribute": "Anomália adatok közreműködése",
       "apply_correction": "Korrekció alkalmazása",
       "copy_alt": {
         "trend_none": "többnyire lapos",
diff --git a/i18n/locales/id-ID.json b/i18n/locales/id-ID.json
index 1ddcf9a3f5..f934642716 100644
--- a/i18n/locales/id-ID.json
+++ b/i18n/locales/id-ID.json
@@ -403,11 +403,6 @@
       "smoothing": "Penghalusan",
       "known_anomalies": "Anomali yang diketahui",
       "known_anomalies_description": "Menyisipkan lonjakan unduhan yang diketahui akibat bot atau masalah CI.",
-      "known_anomalies_ranges": "Batas anomali",
-      "known_anomalies_range": "Dari {start} hingga {end}",
-      "known_anomalies_range_named": "{packageName}: dari {start} hingga {end}",
-      "known_anomalies_none": "Tidak ada anomali yang diketahui untuk paket ini. | Tidak ada anomali yang diketahui untuk paket-paket ini.",
-      "known_anomalies_contribute": "Berkontribusilah pada data anomali",
       "apply_correction": "Terapkan koreksi",
       "copy_alt": {
         "trend_none": "sebagian besar datar",
diff --git a/i18n/locales/ja-JP.json b/i18n/locales/ja-JP.json
index ff5d8ca528..e891990a8f 100644
--- a/i18n/locales/ja-JP.json
+++ b/i18n/locales/ja-JP.json
@@ -460,11 +460,6 @@
       "smoothing": "スムージング",
       "known_anomalies": "既知のアノマリー",
       "known_anomalies_description": "ボットやCIの問題による既知のダウンロードスパイクを補完します。",
-      "known_anomalies_ranges": "アノマリー範囲",
-      "known_anomalies_range": "{start} から {end}",
-      "known_anomalies_range_named": "{packageName}: {start} から {end}",
-      "known_anomalies_none": "このパッケージに既知のアノマリーはありません。|これらのパッケージに既知のアノマリーはありません。",
-      "known_anomalies_contribute": "アノマリーデータの提供",
       "apply_correction": "補正を適用",
       "copy_alt": {
         "trend_none": "ほぼ横ばい",
diff --git a/i18n/locales/pl-PL.json b/i18n/locales/pl-PL.json
index 17632b0018..752d449480 100644
--- a/i18n/locales/pl-PL.json
+++ b/i18n/locales/pl-PL.json
@@ -403,11 +403,6 @@
       "smoothing": "Wygładzanie",
       "known_anomalies": "Znane anomalie",
       "known_anomalies_description": "Interpoluje dane, pomijając znane skoki ilości pobrań spowodowane botami lub problemami z CI",
-      "known_anomalies_ranges": "Zakresy anomalii",
-      "known_anomalies_range": "Od {start} do {end}",
-      "known_anomalies_range_named": "{packageName}: od {start} do {end}",
-      "known_anomalies_none": "Brak znanych anomalii dla tego pakietu. | Brak znanych anomalii dla tych pakietów.",
-      "known_anomalies_contribute": "Dodaj dane o anomaliach",
       "apply_correction": "Zastosuj poprawki",
       "copy_alt": {
         "trend_none": "przeważnie płaski",
diff --git a/i18n/locales/ru-RU.json b/i18n/locales/ru-RU.json
index 11e6c3336a..7b3b61dd3c 100644
--- a/i18n/locales/ru-RU.json
+++ b/i18n/locales/ru-RU.json
@@ -460,11 +460,6 @@
       "smoothing": "Сглаживание",
       "known_anomalies": "Известные аномалии",
       "known_anomalies_description": "Интерполирует данные поверх известных всплесков загрузок, вызванных ботами или проблемами CI.",
-      "known_anomalies_ranges": "Диапазоны аномалий",
-      "known_anomalies_range": "С {start} по {end}",
-      "known_anomalies_range_named": "{packageName}: с {start} по {end}",
-      "known_anomalies_none": "Нет известных аномалий для этого пакета. | Нет известных аномалий для этих пакетов. | Нет известных аномалий для этих пакетов.",
-      "known_anomalies_contribute": "Предложить данные об аномалиях",
       "apply_correction": "Применить корректировку",
       "copy_alt": {
         "trend_none": "в основном без изменений",
diff --git a/i18n/locales/tr-TR.json b/i18n/locales/tr-TR.json
index a761262ae4..d9598af5e7 100644
--- a/i18n/locales/tr-TR.json
+++ b/i18n/locales/tr-TR.json
@@ -460,11 +460,6 @@
       "smoothing": "Yumuşatma",
       "known_anomalies": "Bilinen anomaliler",
       "known_anomalies_description": "npm kayıt defterinde bilinen veri anomalileri",
-      "known_anomalies_ranges": "Etkilenen tarih aralıkları",
-      "known_anomalies_range": "{start} - {end}",
-      "known_anomalies_range_named": "{name}: {start} - {end}",
-      "known_anomalies_none": "Bu paket için bilinen anomali yok",
-      "known_anomalies_contribute": "Anomali bildirin",
       "apply_correction": "Düzeltme uygula",
       "copy_alt": {
         "trend_none": "esas olarak sabit",
diff --git a/i18n/locales/uk-UA.json b/i18n/locales/uk-UA.json
index 1c46738e7b..8a22fa3de3 100644
--- a/i18n/locales/uk-UA.json
+++ b/i18n/locales/uk-UA.json
@@ -460,11 +460,6 @@
       "smoothing": "Згладжування",
       "known_anomalies": "Відомі аномалії",
       "known_anomalies_description": "Інтерполює відомі стрибки кількості завантажень, спричинені ботами або проблемами CI.",
-      "known_anomalies_ranges": "Діапазони аномалій",
-      "known_anomalies_range": "Від {start} до {end}",
-      "known_anomalies_range_named": "{packageName}: від {start} до {end}",
-      "known_anomalies_none": "Для цього пакету немає відомих аномалій. | Для цих пакетів немає відомих аномалій.",
-      "known_anomalies_contribute": "Додати дані про аномалію",
       "apply_correction": "Застосувати корекцію",
       "copy_alt": {
         "trend_none": "здебільшого рівна",
diff --git a/i18n/locales/zh-CN.json b/i18n/locales/zh-CN.json
index 4e91d82823..9d97569c47 100644
--- a/i18n/locales/zh-CN.json
+++ b/i18n/locales/zh-CN.json
@@ -460,11 +460,6 @@
       "smoothing": "平滑处理",
       "known_anomalies": "已知异常",
       "known_anomalies_description": "对已知的由机器人或CI问题导致的下载峰值进行插值处理。",
-      "known_anomalies_ranges": "异常区间",
-      "known_anomalies_range": "{start} 至 {end}",
-      "known_anomalies_range_named": "{packageName}：从 {start} 到 {end}",
-      "known_anomalies_none": "此包没有已知异常。 | 这些包没有已知异常。",
-      "known_anomalies_contribute": "贡献异常数据",
       "apply_correction": "应用校正",
       "copy_alt": {
         "trend_none": "平稳",
diff --git a/i18n/locales/zh-TW.json b/i18n/locales/zh-TW.json
index 231abb7f48..32b15388d3 100644
--- a/i18n/locales/zh-TW.json
+++ b/i18n/locales/zh-TW.json
@@ -421,11 +421,6 @@
       "smoothing": "平滑化",
       "known_anomalies": "已知異常",
       "known_anomalies_description": "針對由機器人或 CI 問題造成的已知下載尖峰進行內插修正。",
-      "known_anomalies_ranges": "異常區間",
-      "known_anomalies_range": "從 {start} 到 {end}",
-      "known_anomalies_range_named": "{packageName}：從 {start} 到 {end}",
-      "known_anomalies_none": "此套件沒有已知異常。 | 這些套件沒有已知異常。",
-      "known_anomalies_contribute": "回報異常資料",
       "apply_correction": "套用修正",
       "copy_alt": {
         "trend_none": "平穩",
diff --git a/i18n/schema.json b/i18n/schema.json
index 1ee624a990..d6ea28a53a 100644
--- a/i18n/schema.json
+++ b/i18n/schema.json
@@ -1420,21 +1420,6 @@
             "known_anomalies_description": {
               "type": "string"
             },
-            "known_anomalies_ranges": {
-              "type": "string"
-            },
-            "known_anomalies_range": {
-              "type": "string"
-            },
-            "known_anomalies_range_named": {
-              "type": "string"
-            },
-            "known_anomalies_none": {
-              "type": "string"
-            },
-            "known_anomalies_contribute": {
-              "type": "string"
-            },
             "apply_correction": {
               "type": "string"
             },

From 7dc8c0bedc188f058b10b91036cdba32f463861b Mon Sep 17 00:00:00 2001
From: Matthew Phillips <matthew@matthewphillips.info>
Date: Wed, 11 Mar 2026 18:03:19 -0400
Subject: [PATCH 4/6] Fix false positives for boundary points and low-volume
 packages

Skip points without a full symmetric window to avoid flattening real
growth at series edges ("great start" problem). Use a relative check
when MAD is 0 instead of flagging any deviation, so sparse packages
like [0,0,0,1,0,0,0] keep their real activity.
---
 app/utils/download-anomalies.ts               | 18 ++++++---
 .../unit/app/utils/download-anomalies.spec.ts | 38 +++++++++++++++++++
 2 files changed, 50 insertions(+), 6 deletions(-)

diff --git a/app/utils/download-anomalies.ts b/app/utils/download-anomalies.ts
index 16e8c8ee19..591a6b9fb1 100644
--- a/app/utils/download-anomalies.ts
+++ b/app/utils/download-anomalies.ts
@@ -45,10 +45,12 @@ export function applyHampelCorrection(
   // Clone to avoid mutating the original data.
   const result = (data as Array<Record<string, any>>).map(d => ({ ...d }))
 
-  for (let i = 0; i < values.length; i++) {
-    // Build a sliding window around the current point, clamped to array bounds.
-    const start = Math.max(0, i - halfWindow)
-    const end = Math.min(values.length - 1, i + halfWindow)
+  // Only evaluate points that have a full symmetric window.
+  // Boundary points lack enough context on one side, making them
+  // prone to false positives (e.g., a "great start" at the end of a series).
+  for (let i = halfWindow; i < values.length - halfWindow; i++) {
+    const start = i - halfWindow
+    const end = i + halfWindow
     const window = values.slice(start, end + 1)
 
     // The median is robust to outliers — unlike the mean, a single spike
@@ -63,9 +65,13 @@ export function applyHampelCorrection(
     const deviation = Math.abs(values[i]! - windowMedian)
 
     // MAD of 0 means most values in the window are identical.
-    // If this point differs from the median at all, it's an outlier.
+    // We can't use the standard MAD-based score here, so fall back to a
+    // relative check: only flag if the deviation is large relative to the
+    // median. When the median is 0, there's no baseline to measure against
+    // so we skip — this avoids erasing real low-volume activity like
+    // [0,0,0,1,0,0,0].
     if (windowMad === 0) {
-      if (deviation > 0) {
+      if (windowMedian > 0 && deviation > windowMedian * threshold) {
         result[i]!.value = Math.round(windowMedian)
         result[i]!.hasAnomaly = true
       }
diff --git a/test/unit/app/utils/download-anomalies.spec.ts b/test/unit/app/utils/download-anomalies.spec.ts
index 6dd76f29ad..de6c3e2947 100644
--- a/test/unit/app/utils/download-anomalies.spec.ts
+++ b/test/unit/app/utils/download-anomalies.spec.ts
@@ -67,6 +67,44 @@ describe('applyHampelCorrection', () => {
     expect(result[1]!.value).toBe(1000) // not enough data to detect
   })
 
+  it('does not flatten a "great start" (sudden real growth at the end)', () => {
+    // A package going from zero to real adoption — this is NOT a spike.
+    const data: WeeklyDataPoint[] = [
+      makeWeeklyPoint('2022-11-07', 0),
+      makeWeeklyPoint('2022-11-14', 0),
+      makeWeeklyPoint('2022-11-21', 0),
+      makeWeeklyPoint('2022-11-28', 0),
+      makeWeeklyPoint('2022-12-05', 0),
+      makeWeeklyPoint('2022-12-12', 0),
+      makeWeeklyPoint('2022-12-19', 20000),
+    ]
+
+    const result = applyHampelCorrection(data) as WeeklyDataPoint[]
+
+    // The 20000 should NOT be erased — it's real growth, not an anomaly.
+    expect(result[6]!.value).toBe(20000)
+    expect(result[6]!.hasAnomaly).toBeUndefined()
+  })
+
+  it('does not flatten low-volume real activity', () => {
+    // Sparse package with occasional real downloads
+    const data: WeeklyDataPoint[] = [
+      makeWeeklyPoint('2022-11-07', 0),
+      makeWeeklyPoint('2022-11-14', 0),
+      makeWeeklyPoint('2022-11-21', 0),
+      makeWeeklyPoint('2022-11-28', 1),
+      makeWeeklyPoint('2022-12-05', 0),
+      makeWeeklyPoint('2022-12-12', 0),
+      makeWeeklyPoint('2022-12-19', 0),
+    ]
+
+    const result = applyHampelCorrection(data) as WeeklyDataPoint[]
+
+    // A single download is not an anomaly
+    expect(result[3]!.value).toBe(1)
+    expect(result[3]!.hasAnomaly).toBeUndefined()
+  })
+
   it('does not mutate the original data', () => {
     const data: WeeklyDataPoint[] = [
       makeWeeklyPoint('2022-11-07', 100),

From 88334f4b11e56c5ac4cfda366093bd6a6ac2efd7 Mon Sep 17 00:00:00 2001
From: Matthew Phillips <matthew@matthewphillips.info>
Date: Wed, 11 Mar 2026 18:41:35 -0400
Subject: [PATCH 5/6] Add tweakable Hampel filter sliders to chart UI

Expose halfWindow and threshold as sliders on a second row in the
data correction panel so users can tune the filter interactively.
---
 app/components/Package/TrendsChart.vue        | 40 ++++++++++++++++++-
 .../Package/WeeklyDownloadStats.vue           |  5 ++-
 app/composables/useSettings.ts                |  4 ++
 app/utils/download-anomalies.ts               |  4 +-
 i18n/locales/en.json                          |  2 +
 i18n/schema.json                              |  6 +++
 6 files changed, 56 insertions(+), 5 deletions(-)

diff --git a/app/components/Package/TrendsChart.vue b/app/components/Package/TrendsChart.vue
index 21fcc010fd..08792b00e8 100644
--- a/app/components/Package/TrendsChart.vue
+++ b/app/components/Package/TrendsChart.vue
@@ -977,7 +977,10 @@ const effectiveDataSingle = computed<EvolutionData>(() => {
 
   if (isDownloadsMetric.value && data.length) {
     if (settings.value.chartFilter.anomaliesFixed) {
-      data = applyHampelCorrection(data)
+      data = applyHampelCorrection(data, {
+        halfWindow: settings.value.chartFilter.hampelWindow,
+        threshold: settings.value.chartFilter.hampelThreshold,
+      })
     }
   }
 
@@ -1021,7 +1024,10 @@ const chartData = computed<{
     let data = state.evolutionsByPackage[pkg] ?? []
     if (isDownloadsMetric.value && data.length) {
       if (settings.value.chartFilter.anomaliesFixed) {
-        data = applyHampelCorrection(data)
+        data = applyHampelCorrection(data, {
+          halfWindow: settings.value.chartFilter.hampelWindow,
+          threshold: settings.value.chartFilter.hampelThreshold,
+        })
       }
     }
     const points = extractSeriesPoints(granularity, data)
@@ -1698,6 +1704,36 @@ watch(selectedMetric, value => {
               class="accent-[var(--accent-color,var(--fg-subtle))]"
             />
           </label>
+        </div>
+        <div v-if="showCorrectionControls" class="grid grid-cols-2 sm:flex items-end gap-3">
+          <label class="flex flex-col gap-1 flex-1">
+            <span class="text-2xs font-mono text-fg-subtle tracking-wide uppercase">
+              {{ $t('package.trends.hampel_window') }}
+              <span class="text-fg-muted">({{ settings.chartFilter.hampelWindow }})</span>
+            </span>
+            <input
+              v-model.number="settings.chartFilter.hampelWindow"
+              type="range"
+              min="1"
+              max="10"
+              step="1"
+              class="accent-[var(--accent-color,var(--fg-subtle))]"
+            />
+          </label>
+          <label class="flex flex-col gap-1 flex-1">
+            <span class="text-2xs font-mono text-fg-subtle tracking-wide uppercase">
+              {{ $t('package.trends.hampel_threshold') }}
+              <span class="text-fg-muted">({{ settings.chartFilter.hampelThreshold }})</span>
+            </span>
+            <input
+              v-model.number="settings.chartFilter.hampelThreshold"
+              type="range"
+              min="1"
+              max="10"
+              step="0.5"
+              class="accent-[var(--accent-color,var(--fg-subtle))]"
+            />
+          </label>
           <div class="flex flex-col gap-1 shrink-0">
             <span
               class="text-2xs font-mono text-fg-subtle tracking-wide uppercase flex items-center justify-between"
diff --git a/app/components/Package/WeeklyDownloadStats.vue b/app/components/Package/WeeklyDownloadStats.vue
index 9d636259d1..c91e84f85a 100644
--- a/app/components/Package/WeeklyDownloadStats.vue
+++ b/app/components/Package/WeeklyDownloadStats.vue
@@ -186,7 +186,10 @@ const correctedDownloads = computed<WeeklyDataPoint[]>(() => {
   let data = weeklyDownloads.value as WeeklyDataPoint[]
   if (!data.length) return data
   if (settings.value.chartFilter.anomaliesFixed) {
-    data = applyHampelCorrection(data) as WeeklyDataPoint[]
+    data = applyHampelCorrection(data, {
+      halfWindow: settings.value.chartFilter.hampelWindow,
+      threshold: settings.value.chartFilter.hampelThreshold,
+    }) as WeeklyDataPoint[]
   }
   data = applyDataCorrection(data, settings.value.chartFilter) as WeeklyDataPoint[]
   return data
diff --git a/app/composables/useSettings.ts b/app/composables/useSettings.ts
index 3f23814f14..b0738bc4a8 100644
--- a/app/composables/useSettings.ts
+++ b/app/composables/useSettings.ts
@@ -45,6 +45,8 @@ export interface AppSettings {
     averageWindow: number
     smoothingTau: number
     anomaliesFixed: boolean
+    hampelWindow: number
+    hampelThreshold: number
     predictionPoints: number
   }
 }
@@ -69,6 +71,8 @@ const DEFAULT_SETTINGS: AppSettings = {
     averageWindow: 0,
     smoothingTau: 1,
     anomaliesFixed: true,
+    hampelWindow: 3,
+    hampelThreshold: 3,
     predictionPoints: 4,
   },
 }
diff --git a/app/utils/download-anomalies.ts b/app/utils/download-anomalies.ts
index 591a6b9fb1..58495b87f0 100644
--- a/app/utils/download-anomalies.ts
+++ b/app/utils/download-anomalies.ts
@@ -31,12 +31,12 @@ export function applyHampelCorrection(
 ): EvolutionData {
   // halfWindow controls how many neighbors on each side to consider.
   // A window of 3 means we look at 7 points total (3 left + current + 3 right).
-  const halfWindow = opts?.halfWindow ?? DEFAULT_HALF_WINDOW
+  const halfWindow = opts?.halfWindow || DEFAULT_HALF_WINDOW
 
   // threshold controls sensitivity. A value of 3 means a point must deviate
   // more than 3 scaled MADs from the local median to be flagged.
   // Higher = less sensitive, lower = more aggressive filtering.
-  const threshold = opts?.threshold ?? DEFAULT_THRESHOLD
+  const threshold = opts?.threshold || DEFAULT_THRESHOLD
 
   // Not enough data to form a full window — return as-is.
   if (data.length < halfWindow * 2 + 1) return data
diff --git a/i18n/locales/en.json b/i18n/locales/en.json
index 2c620c970d..1f0f6c2f68 100644
--- a/i18n/locales/en.json
+++ b/i18n/locales/en.json
@@ -470,6 +470,8 @@
       "average_window": "Average window",
       "smoothing": "Smoothing",
       "prediction": "Prediction",
+      "hampel_window": "Hampel window",
+      "hampel_threshold": "Hampel threshold",
       "known_anomalies": "Known anomalies",
       "known_anomalies_description": "Interpolates over known download spikes caused by bots or CI issues.",
       "apply_correction": "Apply correction",
diff --git a/i18n/schema.json b/i18n/schema.json
index d6ea28a53a..7260f078cd 100644
--- a/i18n/schema.json
+++ b/i18n/schema.json
@@ -1414,6 +1414,12 @@
             "prediction": {
               "type": "string"
             },
+            "hampel_window": {
+              "type": "string"
+            },
+            "hampel_threshold": {
+              "type": "string"
+            },
             "known_anomalies": {
               "type": "string"
             },

From bfc1bcb54927522a6d8c57935fd1285f57e3ed0a Mon Sep 17 00:00:00 2001
From: "autofix-ci[bot]" <114827586+autofix-ci[bot]@users.noreply.github.com>
Date: Wed, 11 Mar 2026 22:42:53 +0000
Subject: [PATCH 6/6] [autofix.ci] apply automated fixes

---
 i18n/locales/az-AZ.json | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/i18n/locales/az-AZ.json b/i18n/locales/az-AZ.json
index e0d7893f73..82507f6ef4 100644
--- a/i18n/locales/az-AZ.json
+++ b/i18n/locales/az-AZ.json
@@ -460,11 +460,6 @@
       "smoothing": "Hamarlama",
       "known_anomalies": "Bilinən anomaliyalar",
       "known_anomalies_description": "Botlar və ya CI problemlərindən yaranan bilinən endirmə sıçrayışlarını interpolyasiya edir.",
-      "known_anomalies_ranges": "Anomaliya aralıqları",
-      "known_anomalies_range": "{start}-dən {end}-ə",
-      "known_anomalies_range_named": "{packageName}: {start}-dən {end}-ə",
-      "known_anomalies_none": "Bu paket üçün bilinən anomaliya yoxdur. | Bu paketlər üçün bilinən anomaliya yoxdur.",
-      "known_anomalies_contribute": "Anomaliya məlumatı əlavə et",
       "apply_correction": "Düzəliş tətbiq et",
       "copy_alt": {
         "trend_none": "əsasən sabit",
@@ -1142,11 +1137,11 @@
         "title": "Trendləri Müqayisə Et"
       }
     },
-    "file_too_large": "Fayl müqayisə üçün çox böyükdür",
-    "file_size_warning": "{size} müqayisə üçün 250KB limitini keçir",
     "file_changes": "Fayl Dəyişiklikləri",
     "files_count": "{count} fayl",
     "lines_hidden": "{count} sətir gizlədilib",
+    "file_too_large": "Fayl müqayisə üçün çox böyükdür",
+    "file_size_warning": "{size} müqayisə üçün 250KB limitini keçir",
     "compare_versions": "fərq",
     "compare_versions_title": "Versiyaları müqayisə et",
     "summary": "Xülasə",