# 503 Service Unavailable

> The server is temporarily down or overloaded. The client should retry.

Source: https://apiguide.dev/status-codes/503
Class: server-error
Defined in: RFC 9110, Section 15.6.4 <https://www.rfc-editor.org/rfc/rfc9110.html#section-15.6.4>
Updated: 2026-07-09

## What does HTTP status code 503 mean?

The 503 Service Unavailable status code indicates that the server is temporarily unable to process the request due to planned maintenance or severe overload.

## When to use it in APIs

Use during deployments, maintenance windows, or when database connection pools are exhausted. Always include a `Retry-After` header.

## How it compares to other codes

* **429 Too Many Requests**: Triggered when a *specific* client exceeds their quota. 503 is returned when the *system* itself is overloaded globally.