zod-contract-mock-forge-mcp

Generates deterministic mocks and boundary violations from Zod schemas

An MCP server that turns Zod schemas into mocks, violations, and contract tests — so your AI agent can reason about API contracts without manually crafting payloads.

Zod schemas are runtime code. An AI agent cannot execute them, introspect their constraints, or generate valid/invalid payloads without this layer. The agent also cannot detect when the schema and the OpenAPI docs silently diverged, or whether a schema change breaks existing test fixtures.

npm install -g zod-contract-mock-forge-mcp

Cursor / VS Code (.cursor/mcp.jsonor.vscode/mcp.json)

{ "mcpServers": { "zod-forge": { "command": "zod-contract-mock-forge-mcp" } } }

claude mcp add zod-forge zod-contract-mock-forge-mcp

My schema file is src/schemas/user.ts, exported as UserSchema. My OpenAPI spec is docs/openapi.yaml. 1. introspect_schema — what are the constraints on this schema? 2. generate_mock_variants — give me 10 diverse valid payloads (seed: 42) for CI reproducibility 3. generate_exhaustive_union_violations — test every branch of the role discriminated union 4. detect_schema_drift — has the Zod schema diverged from the OpenAPI docs? 5. evaluate_schema_evolution — does my schema change break any existing mock data?

generate_mock_variants— 3 diverse valid mocks, seeded for CI:

{ "schema_id": "schema_a1b2c3d4", "count": 3, "all_valid": true, "variants": [ { "name": "Colleen Rowe", "age": 37 }, { "name": "Pat Reynolds", "age": 24 }, { "name": "Veronica Konopelski", "age": 45 } ] }

detect_schema_drift— field missing in OpenAPI, extra field in Zod:

{ "drift_count": 2, "drifts": [ { "field_path": "role", "drift_type": "missing_in_openapi", "zod_value": "string", "openapi_value": null }, { "field_path": "email", "drift_type": "missing_in_zod", "zod_value": null, "openapi_value": "string" } ] }

evaluate_schema_evolution— new required field breaks existing mocks:

{ "breaking_change": true, "sample_count": 20, "invalid_mock_count": 20, "failure_reasons": [ { "field_path": "status", "zod_code": "invalid_type", "expected": "string", "received": "undefined", "affected_mock_count": 20 } ] }

npm run build # compile TypeScript → dist/ npm run lint # ESLint npm run format # Prettier --write npm run format:check # Prettier check (used in CI) npm test # Vitest

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