Most API documentation is a generated list of endpoints with parameter tables. It is necessary and it is not sufficient, because it answers what each endpoint accepts and never answers the questions an integrating developer actually has: how do I authenticate, what is the sequence for the thing I am trying to do, and what happens when it goes wrong. The gap between reference and documentation is measured in support tickets.
The single highest-value page is a quickstart that gets someone to a successful call in under ten minutes. Get a key, make one request, see a real response - copy-pasteable, with a working example. That page determines whether a developer evaluating your API forms the impression that this will be easy or that it will be a project, and that impression is formed in the first quarter of an hour.
Then document the workflows rather than the endpoints. Real integrations are sequences: create a customer, attach a payment method, create a subscription, handle the webhook. A developer given eleven endpoints must infer the order and the dependencies, and they will infer some of it wrongly. A page per common task, showing the calls in order with real payloads, removes most of the support burden an API generates.
Document errors as thoroughly as successes, because that is where integrators spend their time. Every error code, what causes it, and specifically what to do about it - is it retryable, is it a client mistake, does it need a different call first. An error reference that says 409 means conflict has told the reader nothing they could not guess.
Real examples beat schemas. A JSON response with plausible values communicates more in five seconds than a table of field types does in a minute, and it lets a developer check their parsing against something concrete. Include the awkward cases too - a paginated response with a cursor, a partial failure, an empty result - since those are the ones people implement wrongly.
Two things keep documentation honest over time. Generate the reference from the same specification the API validates against, so drift is impossible rather than merely discouraged. And test the examples in CI - a documented request that no longer works is worse than no example, and it is the most common decay in any API documentation more than a year old.
