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

# Overview

> What x402 extensions are and how Armory uses them

x402 extensions are protocol-level metadata attached to challenges and payment payloads via the `extensions` object.

Use extensions when a server requires additional fields beyond core payment data, such as authentication, idempotency, or discovery metadata.

## Built-in Extensions

* Sign-In-With-X (`siwx`) for wallet-authenticated access
* Payment Identifier (`paymentIdentifier`) for idempotency
* Bazaar (`bazaar`) for discovery metadata

## Extension Flow

1. Server declares required extensions in `PAYMENT-REQUIRED`
2. Client hooks inspect required extension metadata
3. Client adds extension payload fields before signing
4. Server verifies and processes extension data

## Next Pages

* [Sign-In-With-X](/extensions/siwx)
* [Payment Identifier](/extensions/payment-identifier)
* [Bazaar](/extensions/bazaar)
* [Custom Extensions](/extensions/custom)