old-coder-api

1# old-coder-api
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3Inspired by Sean Goedecke, *Everything I know about good API design* (2025-08-24).
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5This skill covers HTTP/JSON contract and operability concerns. Its compatibility rules assume JSON consumers. For gRPC/protobuf, GraphQL, WebSockets, or another protocol, apply the transport-independent principles only alongside that protocol's own compatibility rules. This is not a substitute for a full application-security review.
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7**Good APIs are boring.** For the people who build them, an API is a product. For the people who use them, it is a tool in the way of something else. Every minute a consumer spends thinking about your API instead of their goal is waste. An interesting API is a bad API — or would be a better one if it were less interesting.
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9Two failure modes an agent falls into by default, and this skill exists to stop both:
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111. **Inventing.** Producing a clever, bespoke interface where the boring conventional one would do.
122. **Breaking.** Renaming, restructuring, or tightening a field because it reads better now — and silently breaking every downstream caller.
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14**Composition with `old-coder`:** when both skills apply, this skill owns the
15HTTP/JSON contract while `old-coder` owns workflow order, SPEC approval, the
16gauntlet, and EVIDENCE. Run Step 0 and the gates before SPEC approval; put the
17surviving API constraints and risks into SPEC and verify them through the
18gauntlet. For review-only work with no implementation, use this skill's review
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