The Powerduck Blog
Product updates, engineering notes, and guides for designing, debugging, testing, mocking, and serving MCP tools from one OpenAPI spec.
Browse the guidesQuick answer: A collection runner like Newman is great at replaying a saved set of requests, but it tests the collection, not the contract. When teams want assertions that stay
Read articleQuick answer: A default in OpenAPI documents what a server or client may assume when a property is absent, but it is not a validation instruction and it does not
Read articleQuick answer: An OpenAPI schema with additionalProperties describes a free-form map keyed by strings, and how a code generator turns that into typed code varies a lot between languages and
Read articleQuick answer: An MCP tool with a loose input schema — everything typed as a string, required fields left unmarked, or a catch-all object — pushes validation to runtime and invites the
Read articleQuick answer: Tests that pass only when run in a certain order are sharing mutable state, and the most common culprit is a fixture that one test mutates and a
Read articleQuick answer: Outbound webhooks invert the usual testing problem: your system is the caller, and you need a receiver that accepts signed payloads, verifies the signature, and behaves like a
Read articleQuick answer: A 400 that only appears when a query value contains a space or a special character is usually double percent-encoding. The client encodes once, then a helper or
Read articleQuick answer: If a file is produced by a generator, any hand edit inside it is borrowed time. The next build rewrites the file from its source of truth and
Read articleQuick answer: Many APIs are not pure request-response: the response to a second call depends on what the first call did, and a stateless mock that always returns the same
Read articleQuick answer: A mock that only returns instant success cannot test how a client behaves when an API is slow, times out, or fails intermittently — and those paths are where
Read articleQuick answer: Splitting an OpenAPI document across files is the right move for large APIs, but every tool that consumes the spec — docs, mock servers, code generators, gateways — needs a
Read articleQuick answer: Versioned documentation is only worth its complexity if you actually support multiple live API versions; for a single evolving API, a well-managed deprecation policy with one current spec
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