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 When an agent chains several API calls into one workflow, a failure midway leaves the system in a partial state that the agent is bad at reasoning about.
Read articleQuick answer Data-driven testing means running the same request and assertion logic against many input rows rather than copying a test for each case. Cloud clients popularized this with a
Read articleQuick answer OpenAPI links let you declare that a value in one response is meant to be used in a later request, connecting operations into a flow instead of leaving
Read articleQuick answer Circular references in an OpenAPI spec, where a model points back to itself directly or through a chain, are legal and common, but they expose the weakest part
Read articleQuick answer A long-running MCP tool that gives no feedback turns the agent into a black box. The agent cannot tell whether the tool is working, has stalled, or should
Read articleQuick answer Tests that insert rows with hardcoded primary keys, like a fixed customer id of 1001, pass on an empty database and fail the moment they run against a
Read articleQuick answer A mock that always returns a happy 200 cannot test the one thing that makes real clients fragile: what happens when the server never responds. Timeouts, retries, backoff,
Read articleQuick answer If your client sends a POST with a JSON body and the server responds with a 302, most HTTP clients follow the redirect automatically and reissue the request
Read articleQuick answer When an agent resolves a merge conflict, do not trust a cleanly completed merge. The default behavior of most coding agents is to make the conflict disappear, not
Read articleAsked to reconcile a list, the agent wrote a per-item loop over a single endpoint. Three-row fixtures looked fast; staging fired hundreds of calls and throttled, even though a bulk endpoint already existed. Check for a batch path before writing the loop.
Read articleQuick answer: Dynamic response templating is powerful precisely because it can echo parts of the request back into the response, which makes it easy to overfit tests to clever stub
Read articleQuick answer: GraphQL goes over a single endpoint, so mocking it as a handful of hand-wired REST-style routes misses the point: a client selects different fields and operations on the
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