The Powerduck Blog
Product updates, engineering notes, and guides for designing, debugging, testing, mocking, and serving MCP tools from one OpenAPI spec.
Browse the guidesThe 3.1/3.2 line aligned OpenAPI with JSON Schema 2020-12, made null a real type, and cleared the way for proper content negotiation. Here is what to change in existing specs and how streaming endpoints (SSE) fit into a 3.2 document.
Read articleA grounded look at the review gates that keep AI-generated APIs usable: staged plans, granular JSON Patch cards that never overwrite your fields, read-before-edit tools, and deterministic validation.
Read articleThree ways to recover a spec from a running codebase: annotations, traffic recording, and AST scanning. We compare what each extracts across eight languages and 28 frameworks, and why honest gaps beat confident guesses on request bodies.
Read articleThe create call returned 200, the detail view 404s, and cancel accepts an illegal state. Scenario tests chain real calls, pass data between steps, and hand the agent evidence to fix with.
Read articleA folder of requests that each return 200 is not a test suite. A scenario chains requests the way a user walks the product: create, capture, poll, act, assert. Here is how to derive scenarios from an OpenAPI spec and run them against mock then staging.
Read articleMost breaking API changes ship silently: a removed enum value, a field turned nullable, a new required parameter, a tightened status code. OpenAPI diffing in CI classifies changes as breaking or non-breaking, blocks the dangerous ones, and turns API review from memory into a checklist.
Read articleWe pointed Prism, Microcks, Postman mock servers, and a local spec-driven workspace at the same OpenAPI 3.2 document, including an SSE stream. Here is what each handled, what cost money, and where examples quietly became lies.
Read articleA concrete sprint diary: one OpenAPI file drove a local mock with latency and error overrides, a four-step checkout scenario with an HTML report, live docs, derived database tables and a hosted MCP endpoint while the real API did not exist yet.
Read articleFake objects in components demo well and integrate badly. Agree on the coupon validation contract first, then let a spec-driven mock answer real HTTP while the service is still being built.
Read articleModern API docs are a rendered OpenAPI document with search, try-it requests, dark mode, and crawlable HTML. Here is how the hosting options actually compare, from self-hosted renderers to managed portals, and what SEO requires.
Read articleAI agents need tools, and hand-writing MCP wrappers around your API recreates the exact drift problem OpenAPI solved. Powerduck Cloud turns one spec into hosted docs and a ready-to-use MCP endpoint.
Read articleAn OpenAPI document is already a tool catalog. Here is how operations become MCP tools, how auth and streaming map across, and what breaks when you point a generic converter at a real spec.
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