[Reference](/docs) · by task

# Build an API

Routes with one typed input and output, the failures callers see, and the OpenAPI document written for you. Read them in this order. Each page links to the pages around it.

1.  [Route groups](/docs/route-groups)
    
    Every route belongs to a route group: a `routes` declaration with a name and a `prefix:`.
    
2.  [Paths and placeholders](/docs/paths-and-placeholders)
    
    A placeholder in a path is typed where it appears, and reaches what the route runs by its name:
    
3.  [One input](/docs/one-input)
    
    A route reads at most one input, named by `input:`.
    
4.  [Output and status](/docs/output-and-status)
    
    `output:` names what the route answers with: an `Output` type, an object made to be sent to clients.
    
5.  [What a route runs](/docs/what-a-route-runs)
    
    `run:` calls one named action.
    
6.  [Declaring a failure](/docs/declaring-a-failure)
    
    A failure is a way an action or query can fail that its caller is expected to handle, such as a todo that doesn't exist.
    
7.  [Saying what can fail: fails](/docs/saying-what-can-fail-fails)
    
    A function or action lists the failures it can end with after `fails`, in its signature:
    
8.  [How failures reach the client](/docs/how-failures-reach-the-client)
    
    Every failure reaches the client in one envelope: `code`, `message`, `request_id`, and the failure's client fields under `details` (Failures).
    
9.  [Idempotent writes](/docs/idempotent-writes)
    
    A client that retries a write after a timeout can't tell whether the first try worked.
    
10.  [Time limits](/docs/time-limits)
     
     Every route has a deadline: 10 seconds, unless `deadline:` sets another, and never more than 60.
     
11.  [OpenAPI](/docs/openapi)
     
     The compiler writes one OpenAPI 3.1 document per API into `build/openapi/`.
     
12.  [The public API record](/docs/the-public-api-record)
     
     Each API has a committed, readable record of its routes, fields and failure codes: `api/main.jadpo_record` for `main`.