docs: add QA checks documentation

platform/self_hosting/running_with_docker.mdx

@@ -145,3 +145,45 @@ spring:
 ```
 
 Don't forget to change the `POSTGRES_USER`, `POSTGRES_PASSWORD`, `username` and `password` properties to your values.
+
+## Optional: Spelling & Grammar checks (LanguageTool)
+
+Tolgee's [QA Checks](/platform/translation_process/qa_checks) include Spelling and Grammar checks powered by [LanguageTool](https://languagetool.org/). These checks require a separate LanguageTool container.
+
+Add the LanguageTool service to your `docker-compose.yml`:
+
+```yaml title=docker-compose.yaml
+services:
+  app:
+    image: tolgee/tolgee{{dockerTagVersion}}
+    volumes:
+      - ./data:/data
+      - ./config.yaml:/config.yaml
+    ports:
+      - '8080:8080'
+    environment:
+      spring.config.additional-location: file:///config.yaml
+    depends_on:
+      - languagetool
+  languagetool:
+    image: erikvl87/languagetool:6.7
+    environment:
+      - Java_Xms=256m
+      - Java_Xmx=1024m
+```
+
+Then add the LanguageTool URL to your `config.yaml`:
+
+```yaml title=config.yaml
+tolgee:
+  language-tool:
+    url: http://languagetool:8010
+```
+
+Or as an environment variable: `TOLGEE_LANGUAGE__TOOL_URL=http://languagetool:8010`
+
+Once configured, you can enable Spelling and Grammar checks in your project's QA settings (they default to Off).
+
+:::note
+The container loads all language models on startup, which can take a while and uses ~1-1.5 GB of memory. Adjust `Java_Xmx` based on your available resources.
+:::

platform/translation_process/qa_checks.mdx

@@ -0,0 +1,230 @@
+---
+id: qa_checks
+title: Translation QA Checks
+sidebar_label: QA Checks
+image: /img/og-images/platform.png
+description: Automatically detect translation quality issues like missing placeholders, inconsistent punctuation, broken placeholder syntax, spelling and grammar errors with Tolgee's built-in localization QA checks.
+---
+
+import { ScreenshotWrapper } from '../shared/_ScreenshotWrapper';
+import { ScreenRecording } from '../shared/_ScreenRecording';
+
+When managing translations across many languages, it's easy for localization errors to slip through. A translator might accidentally remove a placeholder, break [placeholder syntax](/platform/translation_process/icu_message_format), add extra spaces, or miss punctuation. These translation quality issues are hard to spot manually, especially at scale, and can lead to broken UI, missing data, or confusing user experiences.
+
+QA Checks solve this by automatically validating your translations and flagging potential issues such as missing placeholders, broken placeholder syntax, inconsistent punctuation, spelling and grammar errors, and more. Issues are detected **in real time** as you type and also run in the background when translations are saved or modified in bulk.
+
+<ScreenshotWrapper
+  src="/img/docs/platform/qa-checks/qa_checks_overview.png"
+  alt="Overview of QA checks panel in the translation editor showing detected issues"
+/>
+
+:::info Feature availability
+QA Checks are available in advanced plans. [Upgrade your plan](https://tolgee.io/pricing) to use this feature.
+
+If you use the self-hosted version, you must [set up the license](https://tolgee.io/pricing/self-hosted) to use this feature.
+:::
+
+## Enabling QA Checks
+
+If you would like to start using QA checks, you have to enable them first. To enable QA checks
+
+1. Go to `Project settings`
+2. Find the `QA Checks` section
+3. Toggle QA Checks on
+
+<ScreenRecording
+  src="/img/docs/platform/qa-checks/enable.webm"
+  alt="Enabling QA checks in project settings"
+/>
+
+Once enabled, Tolgee will automatically run checks on all translations in the project. You'll see a progress indicator while the initial check completes.
+
+## Available Check Types
+
+Tolgee provides check types organized into two categories: **general checks** that catch common translation issues, and **syntax checks** that validate the structure of the translation itself.
+
+### General Checks
+
+These checks catch common translation issues such as formatting inconsistencies, missing content, and spelling or grammar errors
+
+| Check | Description |
+|-------|-------------|
+| **Empty translation** | Detects blank or whitespace-only translations |
+| **Spaces mismatch** | Leading/trailing space differences, doubled spaces, non-breaking spaces |
+| **Unmatched new lines** | Missing or extra line breaks compared to the base translation |
+| **Trim check** | Detects leading/trailing spaces or new lines within the base translation |
+| **Character case mismatch** | Capitalization differences (e.g., first letter case) |
+| **Missing numbers** | Numeric values present in the base but missing in the translation |
+| **Spelling** | Spelling errors (off by default) |
+| **Grammar** | Grammar errors (off by default) |
+| **Repeated words** | Consecutive repeated words (e.g., "the the") |
+| **Punctuation mismatch** | Missing, extra, or replaced punctuation marks |
+| **Brackets mismatch** | Missing or extra brackets compared to the base |
+| **Brackets unbalanced** | Unclosed or unopened brackets within the translation |
+| **Special character mismatch** | Missing or extra special characters |
+| **Different URLs** | URLs that are missing, extra, or different from the base |
+| **Key length limit** | Translation exceeds the key's configured [character limit](/platform/translation_keys/keys#character-limit) |
+
+### Syntax Checks
+
+These checks validate the structure and syntax of the translation itself
+
+| Check | Description |
+|-------|-------------|
+| **Inconsistent placeholders** | Variable placeholders (e.g., `{userName}`) missing or extra compared to the base |
+| **Inconsistent HTML** | HTML tags missing or extra compared to the base |
+| **HTML syntax** | Unclosed or unopened HTML tags |
+| **ICU syntax** | Invalid [message format](/platform/translation_process/icu_message_format) (select, plural, choice expressions) |
+
+## Spelling and Grammar Checks
+
+Typos and grammar mistakes in translations are easy to miss during manual review, especially across many languages. The `Spelling` and `Grammar` checks help catch these errors automatically.
+
+Both checks are powered by an external spelling and grammar engine that uses dictionaries and pattern-matching rules. This means they are effective at catching common typos, misspellings, and basic grammar errors, but they have important limitations to be aware of.
+
+### What These Checks Can Do
+
+- Detect common **spelling mistakes** and suggest corrections
+- Flag basic **grammar errors** such as incorrect word forms or agreement issues
+- Provide **one-click corrections** for most detected issues
+
+### What These Checks Cannot Do
+
+These checks use rule-based pattern matching, not contextual understanding. They work best on standard prose and may not perform well in all situations
+
+- **Domain-specific terms, brand names, and abbreviations** are often flagged as errors. Use `Ignore` to dismiss these, or add them to your project [glossary](/platform/glossaries/managing_glossaries) so they are automatically excluded from spelling and grammar results.
+- **Short, non-sentence text** such as button labels, menu items, or single-word translations may trigger irrelevant suggestions. Tolgee already filters out some sentence-level rules (like "capitalize first letter") that don't apply to short text, but occasional false positives are expected.
+- **Language coverage varies.** The engine supports approximately 30 languages, with some having comprehensive rules and others having minimal coverage. If a language is not supported, the checks silently return no results for that language.
+- **Placeholders, HTML, and URLs are excluded.** To reduce noise, issues that overlap with [placeholders](/platform/translation_process/icu_message_format), HTML tags, or URLs are automatically filtered out. Dedicated checks already cover those elements.
+
+### Enable Spelling and Grammar Checks
+
+Both checks default to `Off` because they require additional setup for self-hosted instances and are best enabled intentionally after understanding their limitations.
+
+To enable them, go to `Project settings` > `QA Checks` and set `Spelling` and `Grammar` to `Warning`.
+
+:::note Self-hosted instances
+Spelling and grammar checks require a separate container to run. If you are self-hosting Tolgee, see the [self-hosting setup guide](/platform/self_hosting/running_with_docker#optional-spelling--grammar-checks-languagetool) for deployment instructions. Without it, these checks cannot be enabled.
+:::
+
+## Viewing QA Issues
+
+### In the Translation Editor
+
+To help translators catch issues as they work, QA checks are shown directly in the translation editor. When you open a translation for editing, the QA checks panel appears below the text field. Each issue shows
+
+- The **check type** (e.g., "Spaces mismatch")
+- A **description** of what was detected
+- A **suggested replacement** when available, with highlighted differences
+
+<ScreenRecording
+  src="/img/docs/platform/qa-checks/translations_view.webm"
+  alt="QA checks panel in the translation editor showing issues"
+/>
+
+Issues are updated **in real time** as you type, so you get immediate feedback on your changes.
+
+### Inline Highlights
+
+Problematic text spans are highlighted directly in the translation editor. Hovering over a highlight shows the issue details and a suggested fix.
+
+<ScreenRecording
+  src="/img/docs/platform/qa-checks/inline_highlights.webm"
+  alt="Inline highlights showing issue details on hover"
+/>
+
+### QA Badge
+
+A QA badge appears next to translations in the translations list view when there are open issues or checks are still running
+
+- **Badge with count** - number of open issues
+- **Spinner** - checks are still running (e.g., after an [import](/platform/projects_and_organizations/import) or settings change)
+
+When all issues are resolved, the badge disappears.
+
+<ScreenRecording
+  src="/img/docs/platform/qa-checks/spinner.webm"
+  alt="QA badge showing spinner while checks are running"
+/>
+
+## Fixing Issues
+
+### One-Click Corrections
+
+When a check provides a suggested replacement, you can apply it with a single click on the `Correct` button. The fix is applied directly to the translation text.
+
+<ScreenRecording
+  src="/img/docs/platform/qa-checks/correct.webm"
+  alt="Clicking Correct to apply a suggested fix"
+/>
+
+### Ignoring Issues
+
+Sometimes a flagged issue is intentional or a false positive. For example, you might deliberately omit a placeholder in a specific language, or a grammar check might not understand a domain-specific term. In these cases, you can `Ignore` the issue. Ignored issues won't count toward the issue total and won't appear as warnings.
+
+To ignore an issue, click the `Ignore` button next to it in the QA panel. You can also `Unignore` it later if needed.
+
+<ScreenRecording
+  src="/img/docs/platform/qa-checks/ignore.webm"
+  alt="Ignoring and unignoring a QA issue"
+/>
+
+## Configuring Check Severity
+
+You can customize which checks are active and their severity at both the **project level** and the **language level**.
+
+### Project-Level Settings
+
+To configure QA checks for your entire project
+
+1. Go to `Project settings` > `QA Checks`
+2. For each check type, set the severity
+   - `Warning` - the check is active and issues are reported
+   - `Off` - the check is disabled
+
+*Currently, only two severity levels are supported: `Warning` and `Off`. More severity levels may be added in the future.*
+
+Most checks default to `Warning`. The exceptions are **Spelling** and **Grammar**, which default to `Off`. See [Spelling and Grammar Checks](#spelling-and-grammar-checks) for details on their capabilities and limitations.
+
+:::note Self-hosted: Spelling and Grammar checks
+Spelling and Grammar checks require a separate [LanguageTool](https://languagetool.org/) container. If you are self-hosting Tolgee, see the [self-hosting setup guide](/platform/self_hosting/running_with_docker#optional-spelling--grammar-checks-languagetool) for how to deploy and configure the LanguageTool container. Without it, Spelling and Grammar checks cannot be enabled.
+:::
+
+<ScreenRecording
+  src="/img/docs/platform/qa-checks/project_level_qa_settings.webm"
+  alt="Configuring QA check severity in project settings"
+/>
+
+### Language-Level Overrides
+
+Some checks may not be relevant for all languages. For example, character case checks don't apply to languages without case distinctions, and certain punctuation rules differ across writing systems. Language-level overrides let you fine-tune settings for these cases.
+
+To configure overrides for a specific language
+
+1. Go to `Project settings` > `QA Checks`
+2. Click on the `Language overrides` section
+3. Select a language and adjust the settings
+
+<ScreenRecording
+  src="/img/docs/platform/qa-checks/language_level_qa_settings.webm"
+  alt="Configuring language-level QA check overrides"
+/>
+
+Language-level settings always take precedence over project-level settings. Changing project settings does not affect languages that already have overrides. You can reset a language back to project defaults at any time.
+
+## When QA Checks Run
+
+QA checks run in real time as you type in the translation editor, so you get immediate feedback without saving first. When you save a translation, all enabled checks run again and results are persisted. This also applies to [imported](/platform/projects_and_organizations/import) translations. The QA badge and issue counts are updated accordingly.
+
+The system is designed to handle all rechecking automatically, so you should never need to trigger a manual recheck under normal circumstances. However, as a last resort, you can manually trigger a full QA recheck for all translations in a project from the translations view using [batch operations](/platform/translation_keys/batch_operations).
+
+<ScreenRecording
+  src="/img/docs/platform/qa-checks/recheck_batch.webm"
+  alt="Triggering a full QA recheck via batch operations"
+/>
+
+Checks are also automatically re-run when the base language translation changes, a language tag is changed, or [branches are merged](/platform/branching/merging_branches).
+
+### Plural Translations
+
+For translations that use plural forms, QA checks run separately on each plural variant. Issues are reported per variant, so you can see exactly which form has the problem.

sidebarPlatform.js

@@ -66,6 +66,7 @@ module.exports = {
         'translation_process/labels',
         'translation_process/icu_message_format',
         'translation_process/tolgee_universal_icu_placeholders',
+        'translation_process/qa_checks',
         'translation_process/notifications',
       ],
     },