---
key: docsHome
path: /
section: overview
priority: 1.0
title: Developer documentation
description: How to integrate ZadQ seller attestation into an x402 endpoint, verify a seller from the buyer side, and use the vendorable SDK snippets.
---

# Developer documentation

ZadQ binds an x402 selling endpoint to a legally accountable
operator: an audited legal entity backed by a financial guarantee bond. This
documentation describes how the pieces fit together for integrators — the
seller side, the buyer side, and the SDK.

The service is live and in early operations: endpoint publication and
issuer registration are open.

## The three integration surfaces

| Surface | Who uses it | What it does |
| --- | --- | --- |
| [Seller integration](/integrate-seller) | Operators of x402 selling endpoints | Attach the attestation to HTTP 402 responses |
| [Buyer verification](/verify) | Paying agents and their platforms | Check a seller's attestation locally, free of charge |
| [SDK reference](/sdk) | Both sides | Vendorable snippets with graceful degradation built in |

## Design principles

- **Free verification for the buyer.** The verification path carries no
  charge and no registration requirement.
- **Graceful degradation always.** Every integration keeps working when no
  verdict is available: the badge falls back to the `unknown` state and the
  payment flow proceeds unchanged. Nothing in a third-party product depends
  on reaching ZadQ to function.
- **No personal data.** Attestation concerns legal entities and endpoint
  identifiers. The integration surfaces carry no personal data.
- **Open standards.** "x402" (HTTP 402 Payment Required) is used
  descriptively as the first supported rail; no affiliation is implied.

## Where to start

1. Operating a selling endpoint? Start with the
   [seller integration guide](/integrate-seller).
2. Building a paying agent or a marketplace? Start with
   [buyer verification](/verify).
3. Looking for the code? The [SDK reference](/sdk) lists the vendorable
   modules and their contracts.