Web Application Testing
anthropics/skills
Tests local web applications with Python Playwright scripts, checking frontend behavior, capturing screenshots and reading browser console logs.
Generate mock API servers for testing and development with realistic response data.
Install Mocking APIs
$ npx skills add jeremylongshore/tons-of-skills-marketplace --skill mocking-apis -a claude-codeProject install by default; add -g for ~/.claude/skills/.
$ gh skill install jeremylongshore/tons-of-skills-marketplace mocking-apis --agent claude-codeProject scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).
$ git clone --depth 1 https://github.com/jeremylongshore/tons-of-skills-marketplace.git skills-src && mkdir -p .claude/skills && cp -r skills-src/skills/.curated/mocking-apis .claude/skills/mocking-apis && rm -rf skills-srcUse ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.
Claude Code skills documentation · loads skills from .claude/skills/
Install the "mocking-apis" agent skill from https://github.com/jeremylongshore/tons-of-skills-marketplace/tree/main/skills/.curated/mocking-apis into .claude/skills/mocking-apis/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "mocking-apis", then confirm the skill loads.Claude Code copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$skill-installer install https://github.com/jeremylongshore/tons-of-skills-marketplace/tree/main/skills/.curated/mocking-apisType this inside Codex. $skill-installer <name> installs a curated skill from openai/skills. The installer writes to $CODEX_HOME/skills (default ~/.codex/skills). Restart Codex if the skill does not show up.
$ npx skills add jeremylongshore/tons-of-skills-marketplace --skill mocking-apis -a codexProject install goes to .agents/skills/; add -g for ~/.codex/skills/.
$ gh skill install jeremylongshore/tons-of-skills-marketplace mocking-apis --agent codexProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/jeremylongshore/tons-of-skills-marketplace.git skills-src && mkdir -p .agents/skills && cp -r skills-src/skills/.curated/mocking-apis .agents/skills/mocking-apis && rm -rf skills-srcUse ~/.agents/skills/ instead of .agents/skills for a personal install.
Codex skills documentation · loads skills from .agents/skills/
Install the "mocking-apis" agent skill from https://github.com/jeremylongshore/tons-of-skills-marketplace/tree/main/skills/.curated/mocking-apis into .agents/skills/mocking-apis/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "mocking-apis", then confirm the skill loads.Codex copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ npx skills add jeremylongshore/tons-of-skills-marketplace --skill mocking-apis -a cursorProject install goes to .agents/skills/; add -g for ~/.cursor/skills/.
$ gh skill install jeremylongshore/tons-of-skills-marketplace mocking-apis --agent cursorProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/jeremylongshore/tons-of-skills-marketplace.git skills-src && mkdir -p .cursor/skills && cp -r skills-src/skills/.curated/mocking-apis .cursor/skills/mocking-apis && rm -rf skills-srcUse ~/.cursor/skills/ instead of .cursor/skills for a personal install.
Cursor skills documentation · loads skills from .cursor/skills/, .agents/skills/, .claude/skills/, .codex/skills/
Install the "mocking-apis" agent skill from https://github.com/jeremylongshore/tons-of-skills-marketplace/tree/main/skills/.curated/mocking-apis into .cursor/skills/mocking-apis/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "mocking-apis", then confirm the skill loads.Cursor copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ gemini skills install https://github.com/jeremylongshore/tons-of-skills-marketplace.git --path skills/.curated/mocking-apis--scope user (default) or --scope workspace; --path is the subfolder of the repo that holds the skill; --consent skips the security confirmation prompt.
$ npx skills add jeremylongshore/tons-of-skills-marketplace --skill mocking-apis -a gemini-cliProject install goes to .agents/skills/; add -g for ~/.gemini/skills/.
$ gh skill install jeremylongshore/tons-of-skills-marketplace mocking-apis --agent gemini-cliProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/jeremylongshore/tons-of-skills-marketplace.git skills-src && mkdir -p .gemini/skills && cp -r skills-src/skills/.curated/mocking-apis .gemini/skills/mocking-apis && rm -rf skills-srcUse ~/.gemini/skills/ instead of .gemini/skills for a personal install, then run /skills reload.
Gemini CLI skills documentation · loads skills from .gemini/skills/, .agents/skills/
Install the "mocking-apis" agent skill from https://github.com/jeremylongshore/tons-of-skills-marketplace/tree/main/skills/.curated/mocking-apis into .gemini/skills/mocking-apis/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "mocking-apis", then confirm the skill loads.Gemini CLI copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ gh skill install jeremylongshore/tons-of-skills-marketplace mocking-apisInstalls for Copilot at project scope by default; add --scope user for a personal install. Preview a skill first with gh skill preview. Needs GitHub CLI 2.90.0 or later (public preview).
$ npx skills add jeremylongshore/tons-of-skills-marketplace --skill mocking-apis -a github-copilotProject install goes to .agents/skills/; add -g for ~/.copilot/skills/.
$ git clone --depth 1 https://github.com/jeremylongshore/tons-of-skills-marketplace.git skills-src && mkdir -p .github/skills && cp -r skills-src/skills/.curated/mocking-apis .github/skills/mocking-apis && rm -rf skills-srcUse ~/.copilot/skills/ instead of .github/skills for a personal install. Commit .github/skills so cloud agent and code review can use it.
GitHub Copilot skills documentation · loads skills from .github/skills/, .claude/skills/, .agents/skills/
Install the "mocking-apis" agent skill from https://github.com/jeremylongshore/tons-of-skills-marketplace/tree/main/skills/.curated/mocking-apis into .github/skills/mocking-apis/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "mocking-apis", then confirm the skill loads.GitHub Copilot copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ npx skills add jeremylongshore/tons-of-skills-marketplace --skill mocking-apis -a opencodeOpenCode documents no install command of its own. Project install goes to .agents/skills/; add -g for ~/.config/opencode/skills/.
$ gh skill install jeremylongshore/tons-of-skills-marketplace mocking-apis --agent opencodeProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/jeremylongshore/tons-of-skills-marketplace.git skills-src && mkdir -p .opencode/skills && cp -r skills-src/skills/.curated/mocking-apis .opencode/skills/mocking-apis && rm -rf skills-srcUse ~/.config/opencode/skills/ instead of .opencode/skills for a personal install.
OpenCode skills documentation · loads skills from .opencode/skills/, .claude/skills/, .agents/skills/
Install the "mocking-apis" agent skill from https://github.com/jeremylongshore/tons-of-skills-marketplace/tree/main/skills/.curated/mocking-apis into .opencode/skills/mocking-apis/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "mocking-apis", then confirm the skill loads.OpenCode copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
Facts
- Skill name
mocking-apis- GitHub stars
- 2.8k
- Token cost
- ~1.3k tokens
- SKILL.md length
- 556 words
- Files
- 4 (incl. references)
- Skills in repo
- 3,342
- Repo updated
- First seen
- Licence
- MIT
At a glance
Generate mock API servers for testing and development with realistic response data.
- Works in 8 steps: Read the OpenAPI specification using… → Generate response fixtures for each… → Configure the mock server to match… → …
- Creating mock APIs for development and testing
- SKILL.md covers Overview, Prerequisites, Instructions and Output, plus 3 more sections
- Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md
What it does
Mocking APIs is an agent skill from jeremylongshore/tons-of-skills-marketplace. Generate mock API servers for testing and development with realistic response data. Use when creating mock APIs for development and testing. Trigger with phrases like "create mock API", "generate API mock", or "setup mock server".
Its SKILL.md is about 1.3k tokens, which your agent loads only when the skill is triggered. The skill folder holds 4 other files, including reference files (for example `references/errors.md`, `references/examples.md` and `references/implementation.md`). Compatibility notes: Designed for Claude Code
It sits in Testing & QA. The repository describes itself as: Model-agnostic agent-skills platform with a harness-free canonical layer, verified adapters, and the ccpi package manager. Explore at tonsofskills.com. The licence is MIT.
When your agent uses it
- Creating mock APIs for development and testing
- With phrases like create mock API
- Generate API mock
- Setup mock server
Example prompts
- “create mock API”
- “generate API mock”
- “setup mock server”
- “/mocking-apis”
Requirements
- Node.js
- Docker
- Compatibility (from SKILL.md): Designed for Claude Code
- Pre-approved tools (allowed-tools): Read, Write, Edit, Grep, Glob, Bash(api:mock-*)
Workflow steps
8 steps, taken from the first numbered list in SKILL.md.
- Read the OpenAPI specification using Read and extract all endpoint definitions, response schemas, and example values to build the mock…
- Generate response fixtures for each endpoint using schema-aware data generation: realistic names (Faker), valid emails, properly formatted…
- Configure the mock server to match requests by method, path pattern, query parameters, and request body content type, returning the…
- Add stateful behavior for CRUD operations: POST creates a record in memory, GET returns it, PUT updates it, DELETE removes it -- enabling…
- Implement configurable response delays (50-500ms per endpoint) to simulate real-world latency and test client timeout handling.
- Add error scenario mocking: configure specific request patterns to return 400, 401, 404, 429, or 500 responses for testing error handling…
- Enable request recording that captures all incoming requests with timestamps and headers for later replay in contract tests.
- Create a startup script that launches the mock server on a configurable port with hot-reload when fixture files change.
What it can do on your machine
Read from SKILL.md and the folder at commit cfae287. It shows what the files ask for, not the result of running them.
Tool permissions
Pre-approves these tools, so the agent can use them without asking each time:
ReadWriteEditGrepGlobBash(api:mock-*)
From allowed-tools in the SKILL.md frontmatter.
Runs code
No scripts in the folder and no shell commands in SKILL.md.
From the folder's file list and the shell code blocks in SKILL.md.
Network
Links to these hosts (documentation or services it may open):
stoplight.iomswjs.iowiremock.orgfakerjs.dev
From URLs in SKILL.md, links to its own repository left out.
Credentials
Names no API keys, tokens, secrets or passwords.
From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.
Compatibility
Designed for Claude Code
From compatibility in the SKILL.md frontmatter.
Context cost
Mocking APIs loads about 1.3k tokens when it runs, and up to ~3.3k if it reads all its reference files. Until then it costs about 61 tokens; SKILL.md has 556 words of instructions outside code blocks.
Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.
Safety
Auto-check passed
The automated check found no risky patterns in SKILL.md.
Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.
SKILL.md
The full file from jeremylongshore/tons-of-skills-marketplace at commit cfae287, republished under its MIT licence (© jeremylongshore). 556 words, ~1,271 tokens.
Download SKILL.mdSave it as
.claude/skills/mocking-apis/SKILL.md (or your agent's skills folder). This skill also uses 3 other files; get the full folder from GitHub.- name
- mocking-apis
- description
- Generate mock API servers for testing and development with realistic response data. Use when creating mock APIs for development and testing. Trigger with phrases like "create mock API", "generate API mock", or "setup mock server".
- allowed-tools
- Read, Write, Edit, Grep, Glob, Bash(api:mock-*)
- compatibility
- Designed for Claude Code
- version
- 1.24.0
- author
- Jeremy Longshore <jeremy@intentsolutions.io>
- license
- MIT
- tags
- api, testing, mocking-apis
Mocking APIs
Overview
Generate mock API servers from OpenAPI specifications that return realistic, schema-compliant response data for development and testing. Support dynamic response generation with Faker.js data, configurable latency simulation, stateful CRUD behavior, and request recording for contract testing validation.
Prerequisites
- OpenAPI 3.0+ specification file with response schema definitions
- Mock server runtime: Prism (Stoplight), json-server, MSW (Mock Service Worker), or WireMock
- Faker.js or equivalent for realistic test data generation
- Docker for containerized mock server deployment (optional but recommended)
- Frontend or consumer application needing API stubs for parallel development
Instructions
- Read the OpenAPI specification using Read and extract all endpoint definitions, response schemas, and example values to build the mock response inventory.
- Generate response fixtures for each endpoint using schema-aware data generation: realistic names (Faker), valid emails, properly formatted dates, and relational IDs that reference other mock entities.
- Configure the mock server to match requests by method, path pattern, query parameters, and request body content type, returning the appropriate fixture.
- Add stateful behavior for CRUD operations: POST creates a record in memory, GET returns it, PUT updates it, DELETE removes it -- enabling realistic integration testing flows.
- Implement configurable response delays (50-500ms per endpoint) to simulate real-world latency and test client timeout handling.
- Add error scenario mocking: configure specific request patterns to return 400, 401, 404, 429, or 500 responses for testing error handling paths.
- Enable request recording that captures all incoming requests with timestamps and headers for later replay in contract tests.
- Create a startup script that launches the mock server on a configurable port with hot-reload when fixture files change.
See ${CLAUDE_SKILL_DIR}/references/implementation.md for the full implementation guide.
Output
${CLAUDE_SKILL_DIR}/mocks/server.js- Mock server entry point with route registration${CLAUDE_SKILL_DIR}/mocks/fixtures/- Per-endpoint response fixture JSON files${CLAUDE_SKILL_DIR}/mocks/generators/- Dynamic response generators using Faker.js${CLAUDE_SKILL_DIR}/mocks/scenarios/- Error scenario configurations (4xx, 5xx responses)${CLAUDE_SKILL_DIR}/mocks/state.js- In-memory state store for CRUD behavior${CLAUDE_SKILL_DIR}/mocks/recordings/- Captured request logs for contract testing${CLAUDE_SKILL_DIR}/docker-compose.mock.yml- Docker configuration for mock server
Show full SKILL.md (233 more words)Show less
Error Handling
| Error | Cause | Solution |
|---|---|---|
| Schema mismatch | Mock response does not match updated OpenAPI spec | Run spec-to-fixture sync on spec change; add CI check comparing fixture schemas |
| Missing endpoint | Consumer requests path not defined in OpenAPI spec | Return 501 with message listing available endpoints; log unknown path for spec update |
| Stale fixtures | Mock data becomes unrealistic after API schema evolution | Regenerate fixtures from latest spec; use generators over static fixtures for evolving APIs |
| Port conflict | Mock server port already in use by another dev service | Make port configurable via environment variable; default to spec-defined server URL port |
| State leak between tests | Stateful mock retains data from previous test run | Reset in-memory state before each test suite; expose POST /mock/reset admin endpoint |
Refer to ${CLAUDE_SKILL_DIR}/references/errors.md for comprehensive error patterns.
Examples
Frontend parallel development: Launch a Prism mock server from the OpenAPI spec so frontend developers can build against realistic API responses while backend implementation is in progress.
Integration test isolation: Use MSW (Mock Service Worker) to intercept HTTP requests in Node.js test suites, returning fixture responses without network calls, with per-test response customization.
Contract testing: Record all requests to the mock server during frontend E2E tests, then replay them against the real backend to verify the mock accurately represents actual API behavior.
See ${CLAUDE_SKILL_DIR}/references/examples.md for additional examples.
Resources
- Prism (Stoplight): https://stoplight.io/open-source/prism
- Mock Service Worker (MSW): https://mswjs.io/
- WireMock: https://wiremock.org/
- Faker.js for realistic data generation: https://fakerjs.dev/
© jeremylongshore, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file
Files
SKILL.md and 3 other files (references) in skills/.curated/mocking-apis of jeremylongshore/tons-of-skills-marketplace.
- SKILL.md
- references/errors.md
- references/examples.md
- references/implementation.md
Open the folder on GitHubat commit cfae287
Compare with similar skills
Mocking APIs next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.
| Skill | Stars | Used in | Tokens | Auto-check | Licence | Repo updated |
|---|---|---|---|---|---|---|
| Mocking APIs this skilljeremylongshore/tons-of-skills-marketplace | 2.8k | — | ~1.3k | Automated safety check: Pass | MIT | |
| Web Application Testinganthropics/skills | 180k | 51 repos | ~966 | Automated safety check: Pass | Apache-2.0 | |
| Diagnosing Bugsfossasia/eventyay-interpretation | 1.6k | 32 repos | ~2.1k | Automated safety check: Pass | Apache-2.0 | |
| TDDpietheinstrengholt/rssmonster | 564 | 30 repos | ~906 | Automated safety check: Pass | MIT | |
| TDD WorkflowhellangleZ/burn-in-cceverywhere-ralph | 112 | 11 repos | ~2.4k | Automated safety check: Pass | None | |
| TDDsanity-io/sanity | 6.4k | 20 repos | ~1k | Automated safety check: Pass | MIT |
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Questions about Mocking APIs
What does Mocking APIs do?
Generate mock API servers for testing and development with realistic response data. Mocking APIs is an agent skill from jeremylongshore/tons-of-skills-marketplace. Generate mock API servers for testing and development with realistic response data.
When should I use Mocking APIs?
Mocking APIs fits situations like: creating mock APIs for development and testing; with phrases like create mock API; generate API mock; setup mock server.
How do I install Mocking APIs in Claude Code?
Run `npx skills add jeremylongshore/tons-of-skills-marketplace --skill mocking-apis -a claude-code`. Or copy the skill folder (skills/.curated/mocking-apis in jeremylongshore/tons-of-skills-marketplace) into .claude/skills/mocking-apis in your project. Claude Code loads it when a task matches its description.
How do I install Mocking APIs in Codex?
Run `npx skills add jeremylongshore/tons-of-skills-marketplace --skill mocking-apis -a codex`. Or copy the skill folder (skills/.curated/mocking-apis in jeremylongshore/tons-of-skills-marketplace) into .agents/skills/mocking-apis in your project. Codex loads it when a task matches its description.
Can I use Mocking APIs in Cursor, Gemini CLI or GitHub Copilot?
Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add jeremylongshore/tons-of-skills-marketplace --skill mocking-apis -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/mocking-apis, .gemini/skills/mocking-apis, .github/skills/mocking-apis and .opencode/skills/mocking-apis in your project.
What does Mocking APIs need to run?
SKILL.md names no scripts, command-line tools or credentials: Mocking APIs is instructions for the agent only. Our summary lists: Node.js; Docker. Its frontmatter pre-approves these tools: Read, Write, Edit, Grep, Glob, Bash(api:mock-*). Compatibility (from SKILL.md): Designed for Claude Code.
Does Mocking APIs access the network?
SKILL.md names 4 domains. As links in the text: stoplight.io, mswjs.io, wiremock.org and fakerjs.dev. This is read from the text; nothing was executed.
Is Mocking APIs safe to install?
Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. Review the folder before installing.
What licence does Mocking APIs use?
Mocking APIs is published under the MIT licence (declared in SKILL.md). It allows redistribution, so the full SKILL.md is shown on this page.
How many tokens does Mocking APIs use?
About 1.3k tokens (SKILL.md is roughly 5.1k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full. Its references folder adds about 2k tokens, read only when the agent opens those files.
What are the alternatives to Mocking APIs?
Skills that share tags, products or a category with Mocking APIs: Web Application Testing (anthropics/skills, 180k stars), Diagnosing Bugs (fossasia/eventyay-interpretation, 1.6k stars), TDD (pietheinstrengholt/rssmonster, 564 stars) and TDD Workflow (hellangleZ/burn-in-cceverywhere-ralph, 112 stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.
Who maintains Mocking APIs?
jeremylongshore (a GitHub user) maintains it in jeremylongshore/tons-of-skills-marketplace, which has 2,827 GitHub stars. The repository holds 3,342 skills in this directory. The repository was last updated on October 10, 2026.
Source: jeremylongshore/tons-of-skills-marketplace on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.