agentmods.dev

msw

A guide to MSW v2, a tool that intercepts network requests and returns planned responses during development and testing.

In plain words
What is it for?
Use it when setting up request handlers, mocking REST or GraphQL APIs, isolating tests, checking request matching, or debugging mock responses.
Why use it?
It lets tests cover successful responses, errors, and edge cases without depending on a live REST or GraphQL service.

Skill for Claude CodeCodex

3 12d ago A scan 46 tokens original MIT
View the source file PyModel/react-frontend-skills
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/pymodel/react-frontend-skills/msw
Any agent
npx skills add PyModel/react-frontend-skills --skill msw
Clone the repo
git clone --depth 1 https://github.com/PyModel/react-frontend-skills

Made for: Claude Code, Codex.

Per session 46 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,202 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 $0.00046 $0.01202
Opus 5 $0.00023 $0.00601
Sonnet 5 $0.00009 $0.00240
Haiku 4.5 $0.00005 $0.00120

Measured 2d ago against content hash bd70ee7158b3, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

msw 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 2d ago.

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/msw/SKILL.md · 119 lines

How it starts

The opening of the file, as written. The whole thing — 119 lines — stays where its author put it; the contents beside it link to each section on GitHub.

MSW Best Practices

Comprehensive API mocking guide for MSW v2 applications, designed for AI agents and LLMs. Contains 45 rules across 8 categories, prioritized by impact to guide automated refactoring and code generation.

When to Apply

Reference these guidelines when:

  • Setting up MSW for testing or development
  • Writing or organizing request handlers
  • Configuring test environments with MSW
  • Mocking REST or GraphQL APIs
  • Debugging handler matching issues
  • Testing error states and edge cases

Rule Categories by Priority

Priority Category Impact Prefix
1 Setup & Initialization CRITICAL setup-
2 Handler Architecture CRITICAL handler-
3 Test Integration HIGH test-
4 Response Patterns HIGH response-
5 Request Matching MEDIUM-HIGH match-
6 GraphQL Mocking MEDIUM graphql-
7 Advanced Patterns MEDIUM advanced-
8 Debugging & Performance LOW debug-

Quick Reference

1. Setup & Initialization (CRITICAL)

  • setup-server-node-entrypoint - Use correct entrypoint for Node.js (msw/node)
  • setup-lifecycle-hooks - Configure server lifecycle in test setup
  • setup-worker-script-commit - Commit worker script to version control
  • setup-node-version - Require Node.js 18+ for MSW v2
  • setup-unhandled-requests - Configure unhandled request behavior
  • setup-typescript-config - Configure TypeScript for MSW v2

2. Handler Architecture (CRITICAL)

  • handler-happy-path-first - Define happy path handlers as baseline
  • handler-domain-grouping - Group handlers by domain
  • handler-absolute-urls - Use absolute URLs in handlers
  • handler-shared-resolvers - Extract shared response logic into resolvers
  • handler-v2-response-syntax - Use MSW v2 response syntax
  • handler-request-body-parsing - Explicitly parse request bodies
  • handler-resolver-argument - Destructure resolver arguments correctly
  • handler-reusability-environments - Share handlers across environments

Read the full file on GitHub · 119 lines

Files

What ships with it

48 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. 2d ago First seen · 119 lines · 46 tokens per session scan A bd70ee7158b3

Subscribe to this mod's changes

msw is a skill published in the GitHub repository PyModel/react-frontend-skills (3 stars, last pushed 12d ago), licensed MIT. It adds 46 tokens to every session and 1,202 once invoked, about $0.0002 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 2026-08-31.

Testingagent-skillsai-agentsai-coding-assistantclaude-codecodexcursor
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