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.
npx skills add cyanheads/mcp-ts-core --skill api-testinggit clone --depth 1 https://github.com/cyanheads/mcp-ts-coreWrote 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.
[](https://agentmods.dev/skills/cyanheads/mcp-ts-core/api-testing)<a href="https://agentmods.dev/skills/cyanheads/mcp-ts-core/api-testing"><img src="https://agentmods.dev/badge/skills/cyanheads/mcp-ts-core/api-testing/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/cyanheads/mcp-ts-core/api-testing"><img src="https://agentmods.dev/badge/skills/cyanheads/mcp-ts-core/api-testing.svg" alt="Reviewed on agentmods" width="80" height="20"></a>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.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00046 | $0.07844 |
| Opus 5.5 | $0.00018 | $0.03138 |
| Sonnet 5.5 | $0.00009 | $0.01569 |
| Haiku 4.5 | $0.00005 | $0.00784 |
Grade A, and why
api-testing 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 12d 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.
This is a copy
100% identical to api-testing — 4 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.
How it starts
The opening of the file, as written. The whole thing — 576 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Overview
Tests target handler behavior directly — call handler(input, ctx), assert on the return value or thrown error. The framework's handler factory (try/catch, formatting, telemetry) is not involved. Use createMockContext from @cyanheads/mcp-ts-core/testing to construct the ctx argument.
Additional exports from /testing: createMockSession() binds a mock handler context to an HTTP session; createFetchMock() provides a strict upstream HTTP fake; runToolContract() executes a definition through schema, handler, formatting, enrichment/content, and production-shaped error-envelope checks. createMockLogger() returns a standalone MockContextLogger, createInMemoryStorage(options?) provides a real StorageService backed by InMemoryProvider, and expectInputRequired(run) returns the input_required result a multi-round-trip handler asked for (see Mock inputs).
Other testing subpaths: /testing/vitest (fixtures and conformance suites, below), /testing/fuzz (see Fuzz testing), and /testing/apps, whose renderAppTool renders an app tool's ui:// view against your server (a stdio command or an HTTP URL) in a headless MCP Apps host and reports initialization, errors, CSP violations, the view↔host messages, and screenshots. It needs the optional peers @modelcontextprotocol/client and @modelcontextprotocol/ext-apps plus a chrome-headless-shell build; the field-test skill covers installing one and reading the report.
Philosophy: Test behavior, not implementation. Refactors should not break tests. Match the repo's existing test layout: fresh scaffolds use tests/, while colocated src/**/*.test.ts files are also supported. Integration tests at I/O boundaries over unit tests of internals.
mcpTest — fixture-based Vitest test
mcpTest is a test.extend-based Vitest test that provides ctx, session, fetchMock, and storage as per-test fixtures — fresh instances for every test, eliminating boilerplate and enforcing isolation automatically. fetchMock is installed as globalThis.fetch only when requested by a test and restored afterward.
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.
- 12d ago Changed 41b57c310db6
- 17d ago Changed · +4 lines 950eca924646
- 23d ago Changed · +32 lines 5a4bd8f46251
- 24d ago Changed · +2 lines e617d8e94e64
- 25d ago Changed · +8 lines 75b830d0423b
- 1mo ago Changed · +2 lines a1c8e82396ba
- 1mo ago First seen · 528 lines · 46 tokens per session scan A 1958f0095306
api-testing is a skill published in the GitHub repository cyanheads/mcp-ts-core (153 stars, last pushed 9d ago), licensed Apache-2.0. It adds 46 tokens to every session and 7,844 once invoked, about $0.0002 per session on Opus 5.5. A static security scan graded it A with 0 findings. It is 100% identical to api-testing, differing in 4 lines, and is treated as a copy.
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