title: Data tools description: Three deterministic data tools: fixed_response returns a stable mapping, sized_response generates exactly N characters, lorem produces seeded fake-Latin text.

Data tools¶

Three tools that produce deterministic outputs. Useful for testing enrichment dedup, response-size handling, and caching boundaries.

fixed_response¶

Returns a deterministic body derived from a key.

Arguments:

Field	Type	Notes
`key`	string	Required. The same key always yields the same body.

Returns:

{
  "key": "hello",
  "hash": "2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824",
  "body": "fixed[hello]: 2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824"
}

hash is sha256(key). body is "fixed[<key>]: <hash>".

What it tests:

Caching. Call twice with the same key; if the gateway caches, the second response should arrive without an audit row at the upstream (verify in mcp-test's audit log).
Enrichment dedup. If the gateway dedups identical responses before enrichment, you can detect that by comparing what reaches the upstream against what the client sees.
Hash stability. hash is reproducible across processes and versions, so cross-environment tests can pin to specific hash values.

sized_response¶

Returns exactly N characters of deterministic content.

Arguments:

Field	Type	Notes
`size`	int	Required. Must be >= 0.

Returns:

{
  "size": 1024,
  "body": "abcdefghij...abcdefghij" // exactly 1024 chars
}

Body is the lowercase ASCII alphabet repeated, truncated/extended to exactly the requested length.

What it tests:

Size limits. Gateways often enforce response-size caps. Bump size until you hit the cap, then back off.
Chunking. Large responses get chunked over the streamable HTTP transport. Use this to verify the gateway forwards multi-chunk responses correctly.
Compression. A 64KB body with high redundancy (the alphabet repeats) compresses well; comparing on-the-wire bytes shows whether the gateway is compressing.

lorem¶

Returns N words of seeded lorem-ipsum text.

Arguments:

Field	Type	Notes
`words`	int	Required. Number of words to generate. Default 50, max 5000.
`seed`	string	Optional. Same seed gives the same output. Empty seed produces non-deterministic output.

Returns:

{
  "words": 50,
  "body": "Excepteur ipsum lorem aliqua ... laborum."
}

The first word is capitalized; the body ends with a period. Word selection uses a PCG generator seeded from FNV-1a hashes of the seed string.

What it tests:

Reproducibility. Two runs with the same (seed, words) produce byte-identical bodies. Useful for assertion-based tests.
Content-type handling. Bodies are realistic prose, which exercises gateway enrichment that's looking for natural-language content.
Word counts. The audit log records response_chars and content_blocks; with lorem you control the input word count precisely.

Determinism guarantee¶

fixed_response and lorem (with seed) commit to byte-identical output across:

Process restarts.
Different machines, different OS / arch.
Different patch versions of the binary (same major version).

If a major-version bump changes the algorithm, the release notes will call it out. Until then, you can hard-code expected hashes and bodies in your gateway tests.