diff --git a/.github/copilot-instructions.md b/.github/copilot-instructions.md
new file mode 100644
index 0000000..def65d5
--- /dev/null
+++ b/.github/copilot-instructions.md
@@ -0,0 +1,46 @@
+# Copilot Instructions for `goark/fetch`
+
+## Project purpose
+
+`fetch` is a small package focused on downloading data from URL endpoints.
+The package should hide common `net/http` idioms and keep calling code simple.
+
+## Design principles
+
+- Prefer explicit, small APIs over feature-rich abstractions.
+- Keep `context.Context` based methods as the default path.
+- Favor composable option functions (`ClientOpts`, `RequestOpts`).
+- Preserve compatibility when possible; avoid breaking public symbols.
+
+## Error handling
+
+- Use `github.com/goark/errs` as the primary internal error handling package.
+- Prefer `errs.Wrap`, `errs.Join`, and `errs.WithContext` over ad-hoc wrapping patterns.
+- Keep `errors.Is` compatibility when returning wrapped errors.
+- Return wrapped errors so callers can use `errors.Is`.
+- Keep sentinel errors stable (`ErrInvalidURL`, `ErrInvalidRequest`, `ErrHTTPStatus`, `ErrNullPointer`).
+- Include useful context values when wrapping errors.
+
+## HTTP behavior
+
+- Continue to use `net/http` as the base implementation.
+- Ensure response body cleanup remains safe and predictable.
+- Keep behavior for non-success HTTP status explicit and documented.
+
+## Coding style
+
+- Write idiomatic Go and keep implementation straightforward.
+- Avoid unnecessary dependencies.
+- Keep comments concise and in English.
+
+## Testing and validation
+
+- Add or update tests for behavior changes.
+- Prefer local validation with Taskfile targets:
+  - `task test`
+  - `task govulncheck`
+
+## Documentation
+
+- Keep `README.md` in sync with public API changes.
+- Include practical examples for GET/POST and error handling.
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
new file mode 100644
index 0000000..43e5071
--- /dev/null
+++ b/.github/workflows/ci.yml
@@ -0,0 +1,44 @@
+name: ci
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+
+permissions:
+  contents: read
+
+jobs:
+  test-and-lint:
+    name: lint and test
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v6
+
+      - uses: actions/setup-go@v6
+        with:
+          go-version-file: go.mod
+          cache-dependency-path: go.sum
+
+      - name: golangci-lint
+        uses: golangci/golangci-lint-action@v9
+        with:
+          version: latest
+          args: --enable gosec
+
+      - name: Test module
+        run: go test -shuffle on ./...
+
+  govulncheck:
+    name: govulncheck
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v6
+
+      - name: Run govulncheck
+        uses: golang/govulncheck-action@v1
+        with:
+          go-version-file: go.mod
+          go-package: ./...
+          repo-checkout: false
diff --git a/.github/workflows/codeql-analysis.yml b/.github/workflows/codeql-analysis.yml
deleted file mode 100644
index 5cbe92f..0000000
--- a/.github/workflows/codeql-analysis.yml
+++ /dev/null
@@ -1,61 +0,0 @@
-name: "CodeQL"
-
-on:
-  push:
-    branches: [main]
-  pull_request:
-    branches: [main]
-  schedule:
-    #        ┌───────────── minute (0 - 59)
-    #        │  ┌───────────── hour (0 - 23)
-    #        │  │ ┌───────────── day of the month (1 - 31)
-    #        │  │ │ ┌───────────── month (1 - 12 or JAN-DEC)
-    #        │  │ │ │ ┌───────────── day of the week (0 - 6 or SUN-SAT)
-    #        │  │ │ │ │
-    #        │  │ │ │ │
-    #        │  │ │ │ │
-    #        *  * * * *
-    - cron: '30 1 * * 0'
-
-jobs:
-  CodeQL-Build:
-    # CodeQL runs on ubuntu-latest, windows-latest, and macos-latest
-    runs-on: ubuntu-latest
-
-    permissions:
-      # required for all workflows
-      security-events: write
-
-      # only required for workflows in private repositories
-      actions: read
-      contents: read
-
-    steps:
-      - name: Checkout repository
-        uses: actions/checkout@v3
-
-      # Initializes the CodeQL tools for scanning.
-      - name: Initialize CodeQL
-        uses: github/codeql-action/init@v2
-        # Override language selection by uncommenting this and choosing your languages
-        # with:
-        #   languages: go, javascript, csharp, python, cpp, java, ruby
-
-      # Autobuild attempts to build any compiled languages (C/C++, C#, Go, or Java).
-      # If this step fails, then you should remove it and run the build manually (see below).
-      - name: Autobuild
-        uses: github/codeql-action/autobuild@v2
-
-      # ℹ️ Command-line programs to run using the OS shell.
-      # 📚 See https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#jobsjob_idstepsrun
-
-      # ✏️ If the Autobuild fails above, remove it and uncomment the following
-      #    three lines and modify them (or add more) to build your code if your
-      #    project uses a compiled language
-
-      #- run: |
-      #     make bootstrap
-      #     make release
-
-      - name: Perform CodeQL Analysis
-        uses: github/codeql-action/analyze@v2
diff --git a/.github/workflows/codeql.yml b/.github/workflows/codeql.yml
new file mode 100644
index 0000000..9db6ba2
--- /dev/null
+++ b/.github/workflows/codeql.yml
@@ -0,0 +1,35 @@
+name: CodeQL
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+    branches:
+      - main
+  schedule:
+    - cron: "0 20 * * 0"
+
+permissions:
+  actions: read
+  contents: read
+  security-events: write
+
+jobs:
+  analyze:
+    name: Analyze
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v6
+
+      - name: Initialize CodeQL
+        uses: github/codeql-action/init@v3
+        with:
+          languages: go
+
+      - name: Autobuild
+        uses: github/codeql-action/autobuild@v3
+
+      - name: Perform CodeQL analysis
+        uses: github/codeql-action/analyze@v3
diff --git a/.github/workflows/lint.yml b/.github/workflows/lint.yml
deleted file mode 100644
index e6ae76f..0000000
--- a/.github/workflows/lint.yml
+++ /dev/null
@@ -1,50 +0,0 @@
-name: lint
-on:
-  push:
-    branches:
-      - main
-  pull_request:
-
-permissions:
-  contents: read
-  # Optional: allow read access to pull request. Use with `only-new-issues` option.
-  # pull-requests: read
-jobs:
-  golangci:
-    name: lint
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v6
-      - uses: actions/setup-go@v6
-        with:
-          go-version-file: 'go.mod'
-      - name: golangci-lint
-        uses: golangci/golangci-lint-action@v9
-        with:
-          # Optional: version of golangci-lint to use in form of v1.2 or v1.2.3 or `latest` to use the latest version
-          version: latest
-
-          # Optional: working directory, useful for monorepos
-          # working-directory: somedir
-
-          # Optional: golangci-lint command line arguments.
-          args: --enable gosec
-
-          # Optional: show only new issues if it's a pull request. The default value is `false`.
-          # only-new-issues: true
-
-          # Optional: if set to true then the all caching functionality will be complete disabled,
-          #           takes precedence over all other caching options.
-          # skip-cache: true
-
-          # Optional: if set to true then the action don't cache or restore ~/go/pkg.
-          # skip-pkg-cache: true
-
-          # Optional: if set to true then the action don't cache or restore ~/.cache/go-build.
-          # skip-build-cache: true
-      - name: testing
-        run: go test -shuffle on ./...
-      - name: install govulncheck
-        run: go install golang.org/x/vuln/cmd/govulncheck@latest
-      - name: running govulncheck
-        run: govulncheck ./...
diff --git a/.github/workflows/vulns.yml b/.github/workflows/vulns.yml
deleted file mode 100644
index d1c8732..0000000
--- a/.github/workflows/vulns.yml
+++ /dev/null
@@ -1,19 +0,0 @@
-name: vulns
-on:
-  push:
-    branches:
-      - main
-  pull_request:
-jobs:
-  vulns:
-    name: Vulnerability scanner
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v5
-      - uses: actions/setup-go@v5
-        with:
-          go-version-file: 'go.mod'
-      - name: WriteGoList
-        run: go list -json -m all > go.list
-      - name: Nancy
-        uses: sonatype-nexus-community/nancy-github-action@main
diff --git a/README.md b/README.md
index 737af72..a28661e 100644
--- a/README.md
+++ b/README.md
@@ -1,54 +1,149 @@
 # [fetch] -- Fetch Data from URL
 
-[![check vulns](https://github.com/goark/fetch/workflows/vulns/badge.svg)](https://github.com/goark/fetch/actions)
-[![lint status](https://github.com/goark/fetch/workflows/lint/badge.svg)](https://github.com/goark/fetch/actions)
-[![GitHub license](https://img.shields.io/badge/license-Apache%202-blue.svg)](https://raw.githubusercontent.com/goark/fetch/master/LICENSE)
+[![ci status](https://github.com/goark/fetch/workflows/ci/badge.svg)](https://github.com/goark/fetch/actions)
+[![codeql status](https://github.com/goark/fetch/workflows/CodeQL/badge.svg)](https://github.com/goark/fetch/actions)
+[![GitHub license](https://img.shields.io/badge/license-Apache%202-blue.svg)](https://raw.githubusercontent.com/goark/fetch/main/LICENSE)
 [![GitHub release](https://img.shields.io/github/release/goark/fetch.svg)](https://github.com/goark/fetch/releases/latest)
 
-This package is required Go 1.25 or later.
+`fetch` is a focused helper package for downloading data from URL endpoints.
+It wraps common `net/http` idioms so callers can handle download flows with less boilerplate and safer defaults.
 
-**Migrated repository to [github.com/goark/fetch][fetch]**
+## Design goals
 
-## Import
+- Keep application code simple for one-shot data fetching.
+- Hide repetitive `net/http` handling patterns.
+- Keep API surface small and composable.
+- Use `context.Context` based operations as the default style.
+
+## Development
+
+### Requirements
+
+- Go 1.25 or later
+- [Task](https://taskfile.dev/) command (local tool for this repository)
+
+### Local validation
+
+```text
+task test
+task govulncheck
+```
+
+Run all maintenance tasks:
+
+```text
+task
+```
+
+## CI Workflows
+
+- `ci`: lint (`golangci-lint` with `gosec`), tests, and `govulncheck`
+- `CodeQL`: scheduled and push/PR static analysis
+
+## Usage
+
+### Install and import
+
+```bash
+go get github.com/goark/fetch@latest
+```
 
 ```go
 import "github.com/goark/fetch"
 ```
 
-## Usage
+### Sample programs
+
+All sample files under `sample/` use the `run` build tag.
+
+```text
+go run -tags run ./sample/sample.go
+```
+
+- Basic GET download: [sample/sample.go](sample/sample.go)
+
+### GET request
 
 ```go
 package main
 
 import (
-    "context"
-    "fmt"
-    "io"
-    "os"
+  "context"
+  "fmt"
+  "io"
+  "os"
 
-    "github.com/goark/fetch"
+  "github.com/goark/fetch"
 )
 
 func main() {
-    u, err := fetch.URL("https://github.com/spiegel-im-spiegel.gpg")
-    if err != nil {
-        fmt.Fprintln(os.Stderr, err)
-        return
-    }
-    resp, err := fetch.New().GetWithContext(context.Background(), u)
-    if err != nil {
-        fmt.Fprintln(os.Stderr, err)
-        return
-    }
-    defer resp.Close()
-    if _, err := io.Copy(os.Stdout, resp.Body()); err != nil {
-        fmt.Fprintln(os.Stderr, err)
-    }
+  u, err := fetch.URL("https://github.com/spiegel-im-spiegel.gpg")
+  if err != nil {
+    fmt.Fprintln(os.Stderr, err)
+    return
+  }
+
+  resp, err := fetch.New().GetWithContext(context.Background(), u)
+  if err != nil {
+    fmt.Fprintln(os.Stderr, err)
+    return
+  }
+  defer resp.Close()
+
+  if _, err := io.Copy(os.Stdout, resp.Body()); err != nil {
+    fmt.Fprintln(os.Stderr, err)
+  }
 }
 ```
 
-## Modules Requirement Graph
+### POST request
 
-[![dependency.png](./dependency.png)](./dependency.png)
+```go
+payload := strings.NewReader("name=alice")
+resp, err := fetch.New().PostWithContext(ctx, u, payload,
+  fetch.WithRequestHeaderSet("Content-Type", "application/x-www-form-urlencoded"),
+)
+if err != nil {
+  return err
+}
+defer resp.Close()
+```
+
+### Public API
+
+- `fetch.URL(raw string)` parses and validates URL input.
+- `fetch.New(opts ...fetch.ClientOpts)` creates a fetch client.
+- `Client.GetWithContext(ctx, u, opts...)` performs GET request.
+- `Client.PostWithContext(ctx, u, payload, opts...)` performs POST request.
+- `fetch.WithHTTPClient(cli)` injects custom `*http.Client`.
+- `fetch.WithRequestHeaderAdd(name, value)` and `fetch.WithRequestHeaderSet(name, value)` apply request headers.
+
+### Error handling
+
+The package wraps errors, so use `errors.Is` for checks against:
 
-[fetch]: https://github.com/goark/fetch "goark/fetch: Fetch Data from URL"
+- `fetch.ErrInvalidURL`
+- `fetch.ErrInvalidRequest`
+- `fetch.ErrHTTPStatus`
+
+```go
+if err != nil {
+  switch {
+  case errors.Is(err, fetch.ErrInvalidURL):
+    // invalid URL input
+  case errors.Is(err, fetch.ErrHTTPStatus):
+    // non-success HTTP status (>= 400)
+  }
+}
+```
+
+### Response lifecycle
+
+Always close the response:
+
+- `defer resp.Close()` for streaming use.
+- Use `resp.DumpBodyAndClose()` when you need body bytes at once.
+
+### Modules Requirement Graph
+
+[![dependency.png](./dependency.png)](./dependency.png)
diff --git a/go.mod b/go.mod
index 2fb1bf1..825f6b9 100644
--- a/go.mod
+++ b/go.mod
@@ -4,4 +4,4 @@ go 1.25
 
 toolchain go1.26.3
 
-require github.com/goark/errs v1.3.3
+require github.com/goark/errs v1.3.4
diff --git a/go.sum b/go.sum
index afafe66..4e63d82 100644
--- a/go.sum
+++ b/go.sum
@@ -1,2 +1,4 @@
 github.com/goark/errs v1.3.3 h1:vqzm/1aqvh4Ha8JDqIqIU5ZoBtjaRezFcMC55B5ljAM=
 github.com/goark/errs v1.3.3/go.mod h1:4xM7rorwYQlqh9kUhfKpC5P7VAJW2KfvuQpYnTaU0ek=
+github.com/goark/errs v1.3.4 h1:/+/xwF3UwXGxGGLurzBTaMMoryTBeaPfheJ1aW9cglA=
+github.com/goark/errs v1.3.4/go.mod h1:4xM7rorwYQlqh9kUhfKpC5P7VAJW2KfvuQpYnTaU0ek=