Api Designer is a skill published by agensi that gives an agent a structured framework for designing and reviewing APIs across REST, GraphQL, and event-driven architectures. Rather than stopping at endpoint sketching, it covers resource modeling, lifecycle states, request and response shapes, and contract-first documentation — all before a line of implementation code is written.
The skill enforces standardized strategies for pagination, error handling, versioning, and naming conventions, applying industry best practices instead of leaving those decisions open to debate. It supports three main workflows: contract-first design, where the agent produces detailed specs including endpoint summaries, auth expectations, and explicit error behaviors; API auditing, where it generates a prioritized list of design risks, severity assessments, and backward compatibility findings with actionable fixes; and integration planning, where it defines authentication boundaries and transport-independent business logic.
Output is structured and high-density, giving development teams a reviewable design artifact rather than informal notes. The skill is suited to teams that need consistent, maintainable API contracts across internal and public-facing services. It does not execute code, connect to databases, or call live endpoints — it operates entirely at the design and documentation layer. There are no required environment variables and no package to install separately; it is consumed as a skill within a compatible agent runtime.