400 Bad Request

Description

The 400 Bad Request status code indicates that the server cannot or will not process the request due to something that is perceived to be a client error. This could be due to malformed request syntax, invalid request message framing, or deceptive request routing.

This status code is commonly used when: - The request contains invalid syntax - The request parameters are invalid - The request body is malformed or cannot be parsed - The request is missing required parameters - The client has sent a request that doesn't comply with the application's expectations

The 400 Bad Request error is a generic client-side error status, indicating that the server understood the content type of the request but was unable to process the contained instructions.

Syntax

The server responds with a 400 Bad Request status and typically includes an explanation of the error:

HTTP/1.1 400 Bad Request
Content-Type: application/json
Content-Length: [length in bytes]

{
  "error": "Bad Request",
  "message": "The request could not be understood by the server due to malformed syntax",
  "details": [specific details about what was wrong with the request]
}

Examples

Malformed JSON Example

A client sends a request with malformed JSON:

Client Request:

POST /api/users HTTP/1.1
Host: api.example.com
Content-Type: application/json
Content-Length: 42

{
  "name": "John Doe",
  "email": "[email protected],
}

Server Response:

HTTP/1.1 400 Bad Request
Content-Type: application/json
Content-Length: 160

{
  "error": "Bad Request",
  "message": "Invalid JSON in request body",
  "details": "Unexpected end of JSON input at line 4 column 1"
}

Missing Required Parameter Example

A client sends a request missing a required parameter:

Client Request:

POST /api/orders HTTP/1.1
Host: shop.example.com
Content-Type: application/json
Content-Length: 45
Authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...

{
  "items": [
    {"product_id": 123, "quantity": 2}
  ]
}

Server Response:

HTTP/1.1 400 Bad Request
Content-Type: application/json
Content-Length: 138

{
  "error": "Bad Request",
  "message": "Missing required parameter",
  "details": "The 'shipping_address' field is required for creating an order"
}

Invalid Parameter Value Example

A client sends a request with an invalid parameter value:

Client Request:

GET /api/products?category=electronics&page=-5&limit=1000 HTTP/1.1
Host: api.example.com

Server Response:

HTTP/1.1 400 Bad Request
Content-Type: application/json
Content-Length: 172

{
  "error": "Bad Request",
  "message": "Invalid parameter values",
  "details": {
    "page": "Must be a positive integer",
    "limit": "Must be between 1 and 100"
  }
}

Summary

The 400 Bad Request status code is a fundamental part of HTTP error handling, providing a standard way to indicate that a client's request cannot be processed due to issues with the request itself. It helps clients understand that they need to modify their request before resubmitting it, rather than indicating a server-side problem. By including specific details about what went wrong, servers can guide clients toward correcting their requests, improving the overall robustness of web applications and APIs.