rspack-tracing

rspack-tracing is a skill for Claude Code, Codex from rstackjs/agent-skills. It costs 56 tokens per session (679 once invoked), scanned A, original, MIT.

A guide for investigating Rspack build errors and slow builds. Rspack is a tool that turns application source code and dependencies into files that can run in a browser or other environment.

In plain words
What is it for?
It helps capture a trace, inspect the final build events, and profile which parts of an Rspack build take the most time.
Why use it?
It helps locate the build stage, plugin, or loader responsible for a failure or performance problem by examining build trace files.

Skill for Claude CodeCodex

Part of the rstack plugin — 29 skills shipped together

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/rstackjs/agent-skills/rspack-tracing
Any agent
npx skills add rstackjs/agent-skills --skill rspack-tracing
Clone the repo
git clone --depth 1 https://github.com/rstackjs/agent-skills

Made for: Claude Code, Codex.

Or install rstack, the plugin that ships this one along with the rest of its 29 skills.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for rspack-tracing

README.md
[![agentmods](https://agentmods.dev/badge/skills/rstackjs/agent-skills/rspack-tracing.svg)](https://agentmods.dev/skills/rstackjs/agent-skills/rspack-tracing)
Your own site
<a href="https://agentmods.dev/skills/rstackjs/agent-skills/rspack-tracing"><img src="https://agentmods.dev/badge/skills/rstackjs/agent-skills/rspack-tracing.svg" alt="Measured on agentmods" height="20"></a>
Per session 56 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 679 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00056 $0.00679
Opus 5 $0.00028 $0.00340
Sonnet 5 $0.00011 $0.00136
Haiku 4.5 $0.00006 $0.00068

Measured today against content hash 5c60a3c5668a, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

rspack-tracing scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured today.

The scan reads SKILL.md. This mod also ships 1 executable file (scripts/analyze_trace.mjs), listed below but not scanned — reading those needs a real analyzer, not pattern matching.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

skills/rspack-tracing/SKILL.md · 76 lines

How it starts

The opening of the file, as written. The whole thing — 76 lines — stays where its author put it; the contents beside it link to each section on GitHub.

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

Read the full file on GitHub · 76 lines

Files

What ships with it

3 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. today Changed 5c60a3c5668a
  2. 5d ago First seen · 76 lines · 56 tokens per session scan A e0735945635b

Subscribe to this mod's changes

rspack-tracing is a skill published in the GitHub repository rstackjs/agent-skills (93 stars, last pushed yesterday), licensed MIT. It adds 56 tokens to every session and 679 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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