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

# API fundamentals

> Authenticate, make a first request, handle responses and failures, and operate Telnyx REST API integrations reliably.

Telnyx REST APIs use the `https://api.telnyx.com/v2` base URL, JSON request and response bodies, and Bearer API-key authentication unless an endpoint reference states otherwise.

<Callout type="info">
  Cloud Storage S3 operations, WebRTC clients, WebSocket APIs, and webhook deliveries use product-specific protocols. Follow the linked product documentation instead of applying the REST conventions on this page universally.
</Callout>

## Start here

Complete these steps before configuring a product integration.

<CardGroup cols={3}>
  <Card title="Create an API key" icon="key" href="/docs/development/api-fundamentals/create-api-keys">
    Create, store, rotate, and revoke server-side credentials.
  </Card>

  <Card title="Make the first request" icon="play" href="/docs/development/api-fundamentals/first-api-request">
    Validate authentication with a safe `GET /balance` request.
  </Card>

  <Card title="Browse the API reference" icon="book-open" href="/api-reference">
    Inspect canonical endpoint contracts and language samples.
  </Card>
</CardGroup>

## Build the integration

<CardGroup cols={2}>
  <Card title="Authentication" icon="shield-keyhole" href="/docs/development/api-fundamentals/authentication">
    Send Bearer credentials and separate REST authentication from product-specific protocols.
  </Card>

  <Card title="Requests and responses" icon="arrow-right-arrow-left" href="/docs/development/api-fundamentals/request-response">
    Select methods, encode JSON, and interpret success and error envelopes.
  </Card>

  <Card title="Pagination, filtering, and sorting" icon="list" href="/docs/development/api-fundamentals/pagination-filtering-sorting">
    Traverse collections using only the query parameters declared by each endpoint.
  </Card>

  <Card title="Errors and troubleshooting" icon="triangle-exclamation" href="/docs/development/api-fundamentals/troubleshooting">
    Diagnose authentication, authorization, validation, throttling, and service failures.
  </Card>

  <Card title="Rate limits and retries" icon="rotate" href="/docs/development/api-fundamentals/reliability/rate-limiting">
    Respect response headers and retry only when the operation is safe.
  </Card>

  <Card title="Webhooks" icon="webhook" href="/docs/development/api-fundamentals/webhooks/receiving-webhooks">
    Verify signatures, acknowledge promptly, and process duplicate deliveries idempotently.
  </Card>
</CardGroup>

## Reference and tools

* [Parameters and field names](/docs/development/api-fundamentals/data-standards/parameters-fields)
* [API versions and deprecations](/docs/development/api-fundamentals/api-versions)
* [General and product-specific error codes](/docs/development/api-fundamentals/api-errors)
* [Server-side SDKs](/docs/development/sdk)
* [Telnyx CLI](/docs/development/cli)
* [Agent-readable API documentation](/docs/development/agent-readable-documentation)
* [Other Telnyx interfaces and retired HTTP APIs](/docs/development/api-fundamentals/legacy-apis)