Add external link checking with lychee

.github/workflows/lint-external-links.yml

@@ -0,0 +1,97 @@
+name: Check External Links
+
+on:
+  # Run weekly on Sundays at 2 AM UTC
+  schedule:
+    - cron: '0 2 * * 0'
+
+  # Allow manual triggering
+  workflow_dispatch:
+
+  # Run on PRs that modify docs (non-blocking)
+  pull_request:
+    branches: [master]
+
+jobs:
+  # Job for PRs: check only changed files
+  check-pr:
+    if: github.event_name == 'pull_request'
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Get changed files
+        id: changed
+        run: |
+          FILES=$(git diff --name-only --diff-filter=AM origin/${{ github.base_ref }}...HEAD -- '*.md' '*.mdx' || true)
+          if [ -z "$FILES" ]; then
+            echo "files=" >> $GITHUB_OUTPUT
+            echo "No markdown files changed"
+          else
+            echo "files<<EOF" >> $GITHUB_OUTPUT
+            echo "$FILES" >> $GITHUB_OUTPUT
+            echo "EOF" >> $GITHUB_OUTPUT
+            echo "Changed files:"
+            echo "$FILES"
+          fi
+
+      - name: Restore lychee cache
+        if: steps.changed.outputs.files != ''
+        uses: actions/cache/restore@v4
+        with:
+          path: .lycheecache
+          key: lychee-cache-
+          restore-keys: lychee-cache-
+
+      - name: Check external links
+        if: steps.changed.outputs.files != ''
+        uses: lycheeverse/lychee-action@v2
+        with:
+          args: --verbose --no-progress ${{ steps.changed.outputs.files }}
+          fail: true
+          jobSummary: true
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+
+  # Job for scheduled/manual runs: check all files, create issue
+  check-full:
+    if: github.event_name == 'schedule' || github.event_name == 'workflow_dispatch'
+    runs-on: ubuntu-latest
+    permissions:
+      issues: write
+
+    steps:
+      - uses: actions/checkout@v4
+
+      # Cache strategy: see lychee.toml for details
+      # - Restore previous cache so successful checks are skipped
+      # - Transient errors (429, 5xx) are excluded from cache and retried
+      # - Save updated cache for next run
+      - name: Restore lychee cache
+        uses: actions/cache/restore@v4
+        with:
+          path: .lycheecache
+          key: lychee-cache-
+          restore-keys: lychee-cache-
+
+      - name: Check external links
+        id: lychee
+        uses: lycheeverse/lychee-action@v2
+        with:
+          args: --verbose .
+          output: ./lychee-report.md
+          format: markdown
+          fail: true
+          jobSummary: true
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Save lychee cache
+        uses: actions/cache/save@v4
+        if: always()
+        with:
+          path: .lycheecache
+          key: lychee-cache-${{ github.run_id }}

.gitignore

@@ -105,3 +105,6 @@ public/og-images/*
 yalc.lock
 /public/doctree.json
 /public/doctree-dev.json
+
+# Lychee cache
+.lycheecache

.lycheeignore

@@ -0,0 +1,58 @@
+# URLs to ignore during external link checking
+# Supports regex patterns - lines starting with # are comments
+# Note: Private IPs (localhost, 10.x, 172.16-31.x, 192.168.x) are handled by exclude_all_private in lychee.toml
+
+# Example/placeholder URLs
+https?://example\.com.*
+https?://your-.*
+https?://.*\.example\..*
+https?://___.*___.*
+
+# Internal Sentry development URLs
+https?://.*\.getsentry\.net.*
+https?://sentry-content-dashboard\.sentry\.dev.*
+
+# Sites known to block automated checkers
+https?://twitter\.com.*
+https?://x\.com.*
+https?://linkedin\.com.*
+https?://www\.linkedin\.com.*
+https?://www\.npmjs\.com.*
+https?://search\.maven\.org.*
+https?://medium\.com.*
+https?://.*\.medium\.com.*
+https?://gitlab\.com/oauth/.*
+https?://docs\.gitlab\.com.*
+https?://dev\.epicgames\.com.*
+https?://docs\.unrealengine\.com.*
+https?://cursor\.com.*
+https?://dash\.cloudflare\.com.*
+https?://www\.freedesktop\.org.*
+
+# TLS compatibility issues (sites work in browser but fail in lychee due to native-tls)
+# bottlepy.org only supports TLS 1.3, incompatible with lychee's TLS backend
+https?://bottlepy\.org.*
+
+# Cloudflare ECH (Encrypted Client Hello) required - fails even with curl/openssl
+https?://help\.revise\.dev.*
+https?://.*\.intercomhelpcenter\.com.*
+
+# Rate-limited sites (may fail intermittently with 429)
+https?://godoc\.org.*
+https?://pkg\.go\.dev.*
+
+# Interactive demos that may not respond to HEAD requests
+https?://demo\.arcade\.software.*
+
+# Private/internal resources
+https?://.*\.notion\.so.*
+https?://www\.notion\.so.*
+https?://github\.com/getsentry/getsentry.*
+https?://github\.com/getsentry/sentry-options-automator.*
+https?://github\.com/getsentry/etl.*
+https?://sentry\.zendesk\.com.*
+
+# Placeholder domains commonly used in docs
+https?://api\.example\.com.*
+https?://your-api-host.*
+https?://empowerplant\.io.*

.pre-commit-config.yaml

@@ -34,3 +34,11 @@ repos:
     rev: v1.39.0
     hooks:
       - id: typos
+  - repo: local
+    hooks:
+      - id: lychee
+        name: Check external links (warn only)
+        entry: bun scripts/lint-external-links.ts
+        language: system
+        files: \.(md|mdx)$
+        verbose: true

lychee.toml

@@ -0,0 +1,58 @@
+# Lychee configuration for external link checking
+# Documentation: https://github.com/lycheeverse/lychee
+
+# Base URL to resolve root-relative links
+base_url = "https://docs.sentry.io"
+
+# Only check HTTP and HTTPS links
+scheme = ["https", "http"]
+
+# Exclude all private IP addresses automatically (localhost, 10.x, 172.16-31.x, 192.168.x, etc.)
+exclude_all_private = true
+
+# Exclude internal links (already handled by lint-404s script)
+exclude = ['^https://docs\.sentry\.io']
+
+# Maximum number of concurrent requests
+max_concurrency = 32
+
+# Maximum number of retries per request
+max_retries = 2
+
+# Request timeout in seconds
+timeout = 30
+
+# Retry wait time in seconds
+retry_wait_time = 2
+
+# User agent (some sites block default user agents)
+user_agent = "Mozilla/5.0 (compatible; Sentry-Docs-Link-Checker; +https://github.com/getsentry/sentry-docs)"
+
+# Accept common status codes that indicate the link works
+# Include 403 (possibly bot blocking) and 418 (freedesktop teapot) to reduce noise
+accept = [200, 201, 202, 203, 204, 206, 301, 302, 308, 403, 418]
+
+# Don't validate URL fragments/anchors (e.g., #section-name)
+# Fragment checking is unreliable: JS-rendered anchors appear broken, and many sites don't validate them
+include_fragments = false
+
+# Only check external links (our internal check handles internal ones)
+include_mail = false
+include_verbatim = false
+
+# Follow redirects
+max_redirects = 10
+
+# Cache settings
+#
+# Strategy: Weekly scheduled runs populate the cache, PR checks consume it.
+# - Successful responses (200, 301, 403, 404) are cached and skipped on subsequent runs
+# - Transient errors (429 rate limits, 5xx server errors) are NOT cached, so they get retried
+# - Cache lifetime is just under 2 weeks so it survives between weekly runs
+#
+# This means each weekly run only re-checks:
+# 1. Links that failed with transient errors last time
+# 2. New links not yet in cache
+cache = true
+max_cache_age = "335h"
+cache_exclude_status = "429, 500.."

scripts/lint-404s/README.md

@@ -63,3 +63,42 @@ The `ignore-list.txt` file contains paths that should be skipped during checking
 
 - `0` - No 404s found
 - `1` - 404s were detected
+
+## External Link Checking
+
+This script only checks **internal links**. External links (to third-party sites) are validated separately using [lychee](https://github.com/lycheeverse/lychee).
+
+### Running Locally
+
+```bash
+# Install lychee
+brew install lychee
+
+# Check all markdown files in the repo
+lychee .
+
+# Check a specific file
+lychee docs/platforms/javascript/index.mdx
+```
+
+### Pre-commit Hook
+
+A pre-commit hook checks external links in changed files (warn-only, won't block commits). Requires lychee to be installed locally.
+
+### CI Workflow
+
+The GitHub workflow (`.github/workflows/lint-external-links.yml`) runs:
+
+- Weekly on a schedule (creates/updates issue with broken links)
+- On PRs (checks changed files only)
+- Manually via workflow dispatch
+
+### Configuration Files
+
+- `lychee.toml` - Lychee configuration
+- `.lycheeignore` - URLs to ignore during checking
+
+### Why Separate from Internal Link Checking?
+
+1. **False positives**: Many external sites block automated checkers
+2. **Different scope**: External checks only run on changed files in PRs; internal checks validate all pages

scripts/lint-external-links.ts

@@ -0,0 +1,40 @@
+/**
+ * Pre-commit hook wrapper for lychee external link checker.
+ * Runs lychee on provided files and warns on broken links without blocking commits.
+ *
+ * Usage: bun scripts/lint-external-links.ts [files...]
+ */
+
+import {spawnSync} from 'child_process';
+
+// Check if lychee is installed
+const versionCheck = spawnSync('lychee', ['--version'], {
+  encoding: 'utf-8',
+  stdio: 'pipe',
+});
+if (versionCheck.error || versionCheck.status !== 0) {
+  console.log('Warning: lychee not installed. Skipping external link check.');
+  console.log(
+    'Install with: brew install lychee (macOS) or cargo install lychee (cross-platform)'
+  );
+  process.exit(0);
+}
+
+const files = process.argv.slice(2);
+if (files.length === 0) {
+  process.exit(0);
+}
+
+// Run lychee on the provided files
+const result = spawnSync('lychee', ['--no-progress', ...files], {
+  stdio: 'inherit',
+  encoding: 'utf-8',
+});
+
+if (result.status !== 0) {
+  console.log('');
+  console.log('⚠️  External link issues found (commit not blocked)');
+}
+
+// Always exit 0 so commit proceeds
+process.exit(0);