API and Interface Design

Define the contract before the implementation. This skill is for public or cross-team interfaces where downstream consumers can depend on every observable behavior, including the ones you did not mean to promise.

When to Use

• Designing a new public HTTP API, CLI command, webhook, SDK surface, or plugin contract
• Changing an existing interface that other teams, tools, or customers already consume
• Clarifying breaking-change policy before implementation starts
• Tightening the interface section of spec-driven-development for a compatibility-sensitive feature

When NOT to Use