API Designer Pro is a skill published by agensi that functions as a virtual API architect for designing, reviewing, and auditing APIs across three paradigms: RESTful resources, GraphQL types and resolvers, and asynchronous event-driven systems.
When given high-level feature requirements, it produces detailed API specifications covering endpoints, schemas, and entity relationships. For existing designs, it performs design audits that surface issues such as improper resource naming, incorrect HTTP verb usage, and missing idempotency guarantees. Rather than producing generic CRUD-oriented output, it applies architectural principles like cursor-based pagination, resource-oriented URI structures, and correct HTTP status code semantics that reflect production realities.
For each design, it generates a tailored security checklist and error catalog, covering the specific risks and failure modes introduced by that particular design. The skill provides specialized templates and rule-sets depending on the paradigm—REST, GraphQL, or event-driven—so the output is structured and appropriate to the target architecture.
The resulting documentation is intended to be developer-ready, meaning it can be directly converted into an OpenAPI specification or used as the basis for code generation. This skill is suited to teams or individual developers who need rigorous, opinionated API design guidance embedded in an agent workflow rather than ad-hoc prompting.