# If-None-Match header

> Makes the request conditional; execution occurs only if the client ETag does not match the server ETag.

Source: https://apiguide.dev/headers/if-none-match
Direction: request
Registered: yes
Defined in: RFC 9110, Section 13.1.2 <https://www.rfc-editor.org/rfc/rfc9110.html#section-13.1.2>
Updated: 2026-10-14

## What is the If-None-Match header?

The `If-None-Match` request header is used mainly for conditional GET requests. The server will send the full resource only if the current ETag on the server does not match the client's ETag.

## API Usage & Best Practices

* **Enable HTTP/CDN Caching**: Essential for optimizing mobile apps or web frontends querying configuration, catalogs, or large asset datasets.
* **Returns 304**: If the ETags match on a `GET` or `HEAD`, return `304 Not Modified` with no body. For any other method a failed condition is `412 Precondition Failed`, which is how `If-None-Match: *` on a `PUT` stops a client from overwriting a resource it believes does not exist yet.

## Examples

```http
GET /v1/leads/lead_123 HTTP/1.1
If-None-Match: W/"3a84e27f01"
```