rstackjs/rspack-tracing
skills/rspack-tracing/SKILL.md
Comprehensive guide and toolkit for diagnosing Rspack build issues. Quickly identify where crashes/errors occur, or perform detailed performance profiling to resolve bottlenecks. Use when the user encounters build failures, slow builds, or wants to optimize Rspack performance.
$ install --global
skillsauthnpx skillsauth add rstackjs/agent-skills rspack-tracingInstall this skill globally with one command. Works with Claude Code, Cursor, and Windsurf.
Security Scan Results
3 of 9 scanners reported clean
Some scanners were skipped, did not run, or reported a non-clean status. Review each row below.
3
Scanners Passed
9
Scanners in report
Clean
TrivyContainer and dependency vulnerability scanner
95%
Clean
SemgrepStatic code analysis for vulnerabilities
95%
Clean
mcp-scan (Snyk)Model Context Protocol security validation
95%
Skipped
Snyk (dep)Open source security scanning
50%
Skipped
Socket.devSupply chain security analysis
50%
Skipped
VirusTotalMulti-engine malware detection
50%
Skipped
CrowdStrikeAdvanced threat intelligence
50%
Skipped
OSV-ScannerOpen Source Vulnerability database check
50%
Skipped
OWASP Dep-Check
50%
Last scanned: Apr 18, 2026, 4:30 AM42.8s4 files scanned
SKILL.md
- name:
- rspack-tracing
- description:
- Comprehensive guide and toolkit for diagnosing Rspack build issues. Quickly identify where crashes/errors occur, or perform detailed performance profiling to resolve bottlenecks. Use when the user encounters build failures, slow builds, or wants to optimize Rspack performance.
Rspack Tracing & Performance Profiling
When to Use This Skill
Use this skill when you need to:
- Diagnose why an Rspack build is slow.
- Understand which plugins or loaders are taking the most time.
- Analyze a user-provided Rspack trace file.
- Guide a user to capture a performance profile.
Workflow
1. Capture a Trace
First, ask the user to run their build with tracing enabled.
# Set environment variables for logging to a file
RSPACK_PROFILE=TRACE RSPACK_TRACE_LAYER=logger RSPACK_TRACE_OUTPUT=./trace.json pnpm build
This will generate a trace file in a timestamped directory like .rspack-profile-{timestamp}-{pid}/trace.json.
See references/tracing-guide.md for more details on configuration.
2. Quick Diagnosis for Crashes/Errors
If the user wants to identify which stage a crash or error occurred in, use tail to quickly view the last events without running the full analysis:
# Navigate to the generated profile directory
cd .rspack-profile-*/
# View the last 20 events to see where the build failed
tail -n 20 trace.json
The last events will show the span names and targets where the build stopped, helping to quickly pinpoint the problematic stage, plugin, or loader.
3. Full Performance Analysis
For detailed performance profiling (not just crash diagnosis), ask the user to run the bundled analysis script on the generated trace file.
# Navigate to the generated profile directory
cd .rspack-profile-*/
# Run the analysis script
node ${CLAUDE_PLUGIN_ROOT}/skills/tracing/scripts/analyze_trace.js trace.json
4. Interpret Results
Use the output from the script to identify bottlenecks. Consult references/bottlenecks.md to map span names to actionable fixes.
5. Locate Slow Plugins
Based on the "Top Slowest Hooks" from the analysis script:
- Identify the Hook: Note the hook name (e.g.,
hook:CompilationOptimizeChunks). - Inspect Configuration: Read
rspack.config.jsorrsbuild.config.ts. - Map Hook to Plugin: Look for plugins and their sources that tap into that specific hook.
- Output: Output the paths, lines and columns of the suspected plugin source code.
Common Scenarios & Quick Fixes
- Bottleneck Reference: Mapping spans to concepts.
- Tracing Guide: Detailed usage of
RSPACK_PROFILE.
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