# Rspack Tracing

> 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.

- **Type:** Skill
- **Install:** `agentstack add skill-rstackjs-agent-skills-rspack-tracing`
- **Verified:** Yes — security-reviewed for prompt injection and unsafe behavior
- **Seller:** [rstackjs](https://agentstack.voostack.com/s/rstackjs)
- **Installs:** 0
- **Category:** [Agent Skills](https://agentstack.voostack.com/c/agent-skills)
- **Latest version:** 0.1.0
- **License:** MIT
- **Upstream author:** [rstackjs](https://github.com/rstackjs)
- **Source:** https://github.com/rstackjs/agent-skills/tree/main/skills/rspack-tracing

## Install

```sh
agentstack add skill-rstackjs-agent-skills-rspack-tracing
```

Requires the [AgentStack CLI](https://agentstack.voostack.com/docs/cli). Works with Claude Code, Cursor, and any MCP-compatible agent.

## About

# 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.

```bash
# 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](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:

```bash
# 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.

```bash
# 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](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](references/bottlenecks.md): Mapping spans to concepts.
- [Tracing Guide](references/tracing-guide.md): Detailed usage of `RSPACK_PROFILE`.

## Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

- **Author:** [rstackjs](https://github.com/rstackjs)
- **Source:** [rstackjs/agent-skills](https://github.com/rstackjs/agent-skills)
- **License:** MIT

Install and usage instructions live in the source repository linked above.

## Pricing

- **Free** — Free

## Security capabilities

Automated source analysis of v0.1.0 — what this tool can access:

- **Network access:** no
- **Filesystem access:** no
- **Shell / process execution:** no
- **Environment & secrets:** no
- **Dynamic code execution:** no

*"Yes" means the capability is present in the source — more access means more to trust, not that it is unsafe.*


## Versions

- **0.1.0** — security scan: passed — Imported from the upstream source.

## Links

- Listing page: https://agentstack.voostack.com/l/skill-rstackjs-agent-skills-rspack-tracing
- Seller: https://agentstack.voostack.com/s/rstackjs
- Browse the marketplace: https://agentstack.voostack.com/browse

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