MCPInstall

rspack-tracing

by rstackjsAI & Agents

Capture or analyze Rspack build traces to locate slow compiler phases, plugins, loaders, or the last events before a build failure.

Installs
279
Last 24h
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Trending rank
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Security
Not audited

Install

Works with every agent the skills CLI supports.

npx skills add https://github.com/rstackjs/agent-skills --skill rspack-tracing
  1. 01

    Install

    Run the command in your project. The CLI asks which agents to install for.

  2. 02

    Describe the task

    Ask your agent for something this skill covers. It loads rspack-tracing automatically when relevant.

  3. 03

    Review the result

    The agent follows the SKILL.md steps, scripts and references bundled with the skill.

SKILL.md

The instructions your agent reads when the skill is triggered.

Rspack tracing & performance profiling

When to use this skill

Use this skill when you need to:

  1. Diagnose why an Rspack build is slow.
  2. Understand which plugins or loaders are taking the most time.
  3. Analyze a user-provided Rspack trace file.
  4. 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 whether to run the bundled scripts/analyze_trace.mjs on the generated trace file. If they agree, resolve it relative to the Skill root while keeping the working directory in the user's project, then run:

# Navigate to the generated profile directory
cd .rspack-profile-*/

# Run the analysis script
node "<skill-root>/scripts/analyze_trace.mjs" 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:

  1. Identify the Hook: Note the hook name (e.g., hook:CompilationOptimizeChunks).
  2. Inspect Configuration: Read rspack.config.js or rsbuild.config.ts.
  3. Map Hook to Plugin: Look for plugins and their sources that tap into that specific hook.
  4. 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.

FAQ

What does the rspack-tracing skill do?

Capture or analyze Rspack build traces to locate slow compiler phases, plugins, loaders, or the last events before a build failure.

How do I install rspack-tracing?

Run npx skills add https://github.com/rstackjs/agent-skills --skill rspack-tracing in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/rspack-tracing/ (personal) or .claude/skills/rspack-tracing/ (project).

Which AI agents can use rspack-tracing?

Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.

Is rspack-tracing safe to install?

No partner security audit is available yet. Skills can run commands and scripts, so read the SKILL.md and any bundled files before installing.

Who maintains rspack-tracing?

It is published by rstackjs in rstackjs/agent-skills. It has 279 recorded installs.

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