rspack-tracing: Design & UI for AI Agents | OpenAgentSkill

Overview

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.

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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 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:

Identify the Hook: Note the hook name (e.g., hook:CompilationOptimizeChunks).
Inspect Configuration: Read rspack.config.js or rsbuild.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.

View source ↗

File metadata

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.

View original text

---
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:

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 whether to run the bundled [`scripts/analyze_trace.mjs`](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:

```bash
# 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](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`.

Review the source

Skill source recorded

Skill instructions are recorded. This is not a runtime test, safety guarantee or compatibility certification.

Review before install: Avoid automatic install

License: MIT

Dependency or permission surface needs review
Permission surface may require sandboxing
SKILL.md has a minor typo: missing period at the end of a sentence in the Quick Diagnosis section.
The script's output format is not fully described in SKILL.md; users may need to infer how to interpret the analysis results.
Quality score needs review
Permission surface needs review: secrets or environment access, shell or command execution
GitHub adoption: 93 GitHub stars
Stars/forks activity: 93 stars, 4 forks; issue activity unavailable in current metadata
Dependency/runtime risk: command execution surface, credential or environment access
Permission surface: secrets or environment access, shell or command execution

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Source & usage notes

Indexed

Repository metadata and review signals are advisory. Popularity, source discovery and successful execution are different facts.

Source repository: rstackjs/agent-skills
License: MIT
Version: 1.0.0
Last GitHub push: Sep 4, 2026
Registry updated: Sep 7, 2026
Instruction path: skills/rspack-tracing/SKILL.md @ 9032c74a72ad

Version reported in registry metadata; check source releases before relying on it.

Quality

66/100

Promising

Trust

57/100

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More details

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Source: rstackjs/agent-skills
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