---
type: Glossary Term
title: "Idempotency-Key header"
description: "An Idempotency-Key is a unique client-generated token attached to an HTTP POST/PATCH request or agent payment invocation so that if an agent retries after a network timeout, the server recognizes the duplicate and returns the original result rather than executing the action or charging the user twice."
resource: "https://agenticweb.wiki/terms/idempotency-key/"
tags: ["glossary", "act"]
status: stable
generated: { by: agenticweb-builder/1.0, at: 2026-10-23T00:00:00Z }
verified: { by: process:agenticweb-engine, at: 2026-10-23T00:00:00Z }
stale_after: 2026-11-22T00:00:00Z
sources:
  - id: ref-1
    resource: "https://github.com/agentic-commerce-protocol/agentic-commerce-protocol"
    last_modified: 2026-04-17T00:00:00Z
---

# Idempotency-Key header

An **`Idempotency-Key`** is a unique client-generated token attached to an HTTP `POST`/`PATCH` request or agent payment invocation so that if an agent retries after a network timeout, the server recognizes the duplicate and returns the original result rather than executing the action or charging the user twice. It is standard across **Agentic Commerce Protocol**, **x402** / **MPP** payment retries, and non-idempotent MCP tool annotations (`idempotentHint: false`). Used by: agentic-commerce-protocol, mpp.

# Knowledge Graph

* **Related standards**: [Agentic Commerce Protocol](/okf/protocols/agentic-commerce-protocol.md), [Machine Payments Protocol](/okf/protocols/mpp.md)

[^ref-1]: https://github.com/agentic-commerce-protocol/agentic-commerce-protocol (https://github.com/agentic-commerce-protocol/agentic-commerce-protocol)