> ## Documentation Index
> Fetch the complete documentation index at: https://docs.bayareatransit.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Request basics

> Authentication, formats, rate limits, common errors, and request-construction quirks.

## Authentication

The public 511 transit endpoints are documented as requiring an `api_key` query parameter.

## Formats

Most transit endpoints support JSON and XML through an optional `format` parameter. Bulk GTFS downloads return zip files, and GTFS-Realtime feeds return protobuf payloads.

## Rate limits

As of the 511 transit page snapshot reviewed on March 25, 2026, the default token limit is documented as `60 requests per 3600 seconds`.

<Warning>
  That limit is low enough that any polling-heavy integration should assume aggressive caching is mandatory.
</Warning>

## Common errors

* `401 Unauthorized` for invalid API keys
* `404 Not Found` when an individual resource cannot be located
* `500 Internal Server Error` when the service cannot process the request

## Parameter casing mismatches

The public transit page and the transit PDF disagree on some parameter names.

* `stoptimetable` is shown on the live page with lowercase `operatorref`, `monitoringref`, `lineref`, `starttime`, and `endtime`, while the PDF uses capitalized SIRI-style names
* `StopMonitoring` uses `stopcode` on the public page, while the PDF shows `stopCode`
* `timetable` uses lowercase `includespecialservice` and `exceptiondate` on the public page, while the PDF shows `IncludeSpecialService` and `ExceptionDate`

<Info>
  Treat the PDF as the best source for semantics and response structure, and the live public page as the best source for the exact request spelling when the two differ.
</Info>