Every API has documentation that nobody reads end to end. An OpenAPI spec might be hundreds of lines describing paths, methods, request and response shapes, and the resources they operate on. It is precise and complete and almost impossible to hold in your head. What you actually want, when you land on a new service, is a picture: what are the main resources, which endpoints touch them, and how do they hang together?
That picture is already latent in the spec. An OpenAPI or similar document is structured data, which means a tool can read it and draw the shape you would otherwise have to reconstruct by hand.
What the spec already tells you
A well-formed API document contains more structure than it looks. From it you can derive:
- Resources, from the schemas and the path segments (users, orders, products).
- Operations, from the methods on each path (list, create, update, delete).
- Relationships, from schema references (an Order references a User and Line Items).
- Grouping, from tags, which usually map to the service's real modules.
Reading that as text is slow. Seeing it as a diagram is instant, and the diagram is where the "oh, that is how it fits together" moment happens.
The workflow
It is genuinely a paste-and-go. Hand the tool your OpenAPI document, and it extracts the resources and relationships and lays them out as editable shapes. From there you do the usual shaping: group by tag, highlight the core resource, hide the endpoints that are noise for this particular diagram.
The spec is the source of truth for the API. Generating the diagram from it means the picture and the contract cannot disagree.
Why derive it instead of drawing it
You could draw an API diagram by hand, and it would be wrong the next time someone adds an endpoint. Deriving it from the spec ties the picture to the contract. When the API changes, you regenerate, and the diagram is current again in seconds. For a service that evolves, that is the difference between documentation people trust and documentation people quietly ignore.
Beyond a single service
The same idea scales up. If you have several services, each with its own spec, you can build a higher-level map: which service owns which resources, and where one calls another. That is the diagram nobody ever has time to keep current by hand, and exactly the one that saves an afternoon during an incident. Let the specs draw it, then shape it into the view your team needs.
Stop reading YAML to understand a service. Paste the spec and read the picture instead.