Specwise MCP server

Let your coding agent check an API contract: validate an OpenAPI document, find the breaking changes between two versions (also against git), and validate JSON Schemas and data.

The server is open source (MIT). It calls the Specwise API, which is paid, with a free plan.

• You use your own key, from RapidAPI or api.market.
• Every tool call is one request on your plan.
• The free Basic plan has 15 requests a month, with a hard limit, so it never runs up a bill.

1. Get a key

marketplace
RapidAPI	plans
api.market	store

2. Add the server to your MCP client

The server runs locally over stdio with uv. Put your key in its environment.

JSON configuration (Claude Desktop, Cursor, VS Code and most clients):

{
  "mcpServers": {
    "specwise": {
      "command": "uvx",
      "args": ["--from", "bytestay-specwise-mcp", "specwise-mcp"],
      "env": { "RAPIDAPI_KEY": "your-rapidapi-key" }
    }
  }
}

Claude Code:

claude mcp add specwise --env RAPIDAPI_KEY=your-rapidapi-key -- uvx --from bytestay-specwise-mcp specwise-mcp

Environment

variable	meaning
RAPIDAPI_KEY	your RapidAPI key
API_MARKET_KEY	your api.market key, used when RAPIDAPI_KEY is not set
BYTESTAY_MARKETPLACE	rapidapi or apimarket, when both keys are set

Up to 0.2.7 the setting was HFL_MARKETPLACE. The old name still works, with a one-line notice on stderr.

Without a key the server still starts. The first tool call then explains where to get one.

Also listed on Glama:

3. Tools

tool	what it does
validate_openapi(spec=… | spec_path=…)	every error with its JSON Pointer, line and column, plus lint warnings (OpenAPI 3.x and Swagger 2.0)
diff_openapi(...)	each change between two OpenAPI 3.x versions is breaking, warning, non-breaking or info, with a semver suggestion
validate_json_schema(schema=… | schema_path=…, instance=… | instance_path=…, draft=None)	checks the schema against its meta-schema and, if given, the data against the schema

diff_openapi takes the two versions in one of three ways:

• base and revision as text;
• base_path and revision_path as files;
• revision_path with base_git_ref. For example, after editing a spec: revision_path="openapi.yaml", base_git_ref="main".

Every tool returns the API's JSON response.

• When the marketplace reports it, quota_remaining is added: the requests left on your plan this month.
• Errors are explained in plain words, with what to do next:
  • key refused, with the link to subscribe;
  • quota reached, with the plans;
  • input the API couldn't process, with the API's reason.

Privacy

• Local files are read only when a tool is given their path. They are sent to the API for that one request.
• The API processes inputs in memory and doesn't store them. See the privacy policy.
• Your key is only sent to the marketplace you chose.

Limits

• Documents up to about 900 KiB each.
• External $refs are not fetched. Bundle multi-file specs first (redocly bundle).
• The diff needs OpenAPI 3.x; Swagger 2.0 can be validated, not diffed.
• The server needs Python 3.10+ (uv installs it for you).

Development

uv venv && uv pip install -e ".[dev]"
.venv/bin/pytest            # unit tests, no network; 100% coverage required
.venv/bin/ruff check src tests scripts

scripts/e2e_stdio.py specwise runs the server over stdio, as a client would, and calls its tools against the real API. It needs RAPIDAPI_KEY or API_MARKET_KEY.

History

Formerly Hybrid Forge Lab. This repository continues hybridforgelab/specwise-mcp under the ByteStay name since November 2026, so the older commits come from there.

Licence

MIT. Specwise itself is a paid API with a free plan, run by ByteStay.