k11 API Functional QA — MCP server & Claude Code plugin

Functional API tests that prove the API did the right thing, down to the database row.

Contract checks tell you an API still has the right shape. They don't tell you whether placing an order charges the right amount, whether cancelling really soft-deletes the row, or whether a malformed request crashes the server. This MCP server lets Claude (or any MCP client) write and run those tests with you:

• User story → multi-step test flow. Chain calls (POST /orders → save the id → GET /orders/{id} → DELETE) with readable YAML and value checks.

• Database checks in the same flow. After the API call, check the row really changed: SELECT status, deleted_at FROM orders WHERE id = :orderId. Read-only by default, with masked columns.

• Negative and boundary tests from the spec, including nested fields and array items: missing required fields, wrong types, values outside enums and min/max/length limits, no credentials, unknown IDs. Every case must get a 4xx, never a 5xx.

• Evidence for every step: the request, response, query, rows and each check, in Markdown (PR comment), JSON and JUnit XML for CI dashboards.

• Guardrails: data-changing calls are refused on production-like environments, database writes only in fixtures and cleanup on allowlisted test databases, secrets only from environment variables and masked everywhere, and requests never leave the environment's host.

• No lock-in: export any flow as plain pytest + httpx code.

Built on the parsers of k11 API Contract QA (OpenAPI 3.x and Swagger 2.0 for test generation and response-schema checks).

See it find real bugs

The demo shop API (demo/shop/) has two planted bugs. Two hand-written flows and one generated negative suite found them, plus one I didn't plant.

1. The order total is wrong only in the API response. order_total.yaml orders two bags at 42.50:

❌ Order total is quantity times price

• place an order for two bags: failed. Response: HTTP 201. ✗ $.total 85.0: expected 85.0, got 42.5

• the database stores 85.00: passed

• order history shows 85.00: passed

The database check shows exactly where the bug is: the stored total is right, and only the POST /orders response is wrong.

2. Malformed input crashes the server. generate_negative_tests("POST /orders") produced 18 cases from the spec. 16 behaved correctly, and two returned HTTP 500:

• ✗ wrong type for items[0].qty is rejected: got 500. A 5xx is a bug.

• ✗ missing required field items[0].qty is rejected: got 500. A 5xx is a bug.

The second crash wasn't planted. It's the same code path, and the generator found it because it tests nested array items, not just top-level fields.

3. The soft delete works, proven in the database. cancel_order.yaml passes all 7 steps, including checks that the row is kept with status = cancelled and a deleted_at timestamp.

Related MCP server: API Testing Platform

A flow

name: Customer cancels an order and it is soft-deleted
fixtures: [customer]                       # seeded in the test database, removed afterwards
steps:
  - name: place an order
    call: POST /orders
    body: { customerId: "${fixture.customer.id}", channel: web, items: [{ sku: HAT-2, qty: 1 }] }
    expect:
      status: 201
      json: { "$.status": pending, "$.total": 15.0, "$.items": { length: 1 } }
    save: { orderId: "$.id" }

  - name: the row is kept and marked deleted
    db: SELECT status, deleted_at FROM orders WHERE id = :orderId
    params: { orderId: "${orderId}" }
    expect: { rows: 1, row: { status: cancelled, deleted_at: { ne: null } } }

cleanup:
  - db: DELETE FROM orders WHERE id = :orderId
    params: { orderId: "${orderId}" }

• Checks (expect): status (201, "2xx", [400, 422]), json paths ($.items[0].qty, $.items[*].sku, $.items.length), headers, body_contains, max_ms, and the response schema from the spec (on by default). Values compare as literals or with operators: eq ne gt gte lt lte approx contains matches length type in exists empty.

• Variables: save from JSON paths, headers (header:Location) or status; use them as ${orderId}. Generators: ${uuid}, ${random_email}, ${random_int}, ${now}, ${today}. Secrets: ${ENV:NAME}.

• Failures: a step that only fails value checks lets the flow continue, to gather more evidence. A wrong status, a 5xx, a blocked write or a missing saved value stops it. continue_on_failure: true runs every step (generated negative suites use it). Cleanup always runs.

Tools

Configure: .qa-mcp/api-test.yaml

spec: openapi.yaml
default_environment: local
environments:
  local:   { base_url: http://localhost:8080 }
  staging: { base_url: https://staging.example.com, allow_writes: true }
  prod:    { base_url: https://api.example.com }        # read-only: writes refused
auth:
  default: { type: bearer, token: "${ENV:API_TOKEN}" }
  # basic: {username, password} · api_key: {header, value} · oauth2: {token_url, client_id, client_secret, scope}
databases:
  main: { url: "${ENV:TEST_DB_URL}", allow_writes: true, mask: [email, card_number] }
fixtures:
  customer:
    db: main
    insert: { table: customers, values: { id: "${uuid}", email: "${random_email}", name: Test Customer } }
    delete: { table: customers, where: { id: "${id}" } }

Databases: SQLite (built in), PostgreSQL (pip install "k11-api-functional-qa-mcp[postgres]"), MySQL/MariaDB ([mysql]) and SQL Server ([mssql]).

Guardrails

In CI

k11-api-functional-qa-mcp run --env staging

It writes api-test-report.md (PR comment), api-test-report.json (evidence) and api-test-junit.xml, sets GitHub Actions outputs and exits non-zero when a flow fails (--fail-on any|failed|never). See docs/api-tests.yml.

Install

Requires Python 3.10+.

/plugin marketplace add K11-Software-Solutions/k11techlab-api-functional-qa-mcp
/plugin install api-functional-qa@k11-api-functional-qa

The plugin adds /api-story-test and /api-negative-tests. To add only the MCP server:

claude mcp add api-functional-qa -- uvx k11-api-functional-qa-mcp

Claude Desktop and other clients: run uvx k11-api-functional-qa-mcp with QA_MCP_ROOT set to your project.

Try the demo

python demo/shop/server.py --port 8080
SHOP_URL=http://127.0.0.1:8080 SHOP_TOKEN=test-token QA_MCP_ROOT=demo/shop k11-api-functional-qa-mcp run

Scope

This server is for functional REST testing with database checks. Related K11 tools:

• Contract and breaking-change checks (REST, GraphQL, gRPC, AsyncAPI, SOAP): k11 API Contract QA

• UI tests: Playwright QA and Selenium QA

• LLM red-teaming: LLM Assure

Not covered: load testing (use k6 or Gatling) and deep fuzzing (use Schemathesis).

Development

python -m venv .venv && .venv/Scripts/pip install -e ".[dev]"   # bin/pip on macOS/Linux
pytest   # values, guardrails, flows against the demo shop, negative tests, export, CLI, MCP (25)

Roadmap

• GraphQL, gRPC and SOAP calls as flow steps

• Java export (REST Assured)

• MongoDB checks

• Schema-driven test data (realistic values per field format)

Built by K11 Software Solutions. Part of the K11 Tech Lab agentic QA series. MIT licensed.