4xx Client Error

HTTP 400 Bad Request

The server cannot process the request due to something perceived to be a client error — malformed syntax, invalid request framing, or deceptive request routing.

Common Causes

  • Malformed JSON or XML in the request body
  • Missing required request parameters
  • Invalid URL encoding or special characters
  • Request body exceeds expected schema

How to Fix

  1. 1Validate request body format (JSON, XML) before sending
  2. 2Check all required parameters are included
  3. 3Verify URL encoding is correct
  4. 4Compare your request against the API documentation

Example

HTTP 400 Bad Request
POST /api/users HTTP/1.1
{ "name": }  ← invalid JSON

→ 400 Bad Request
→ "Unexpected token } in JSON"

Related Client Error Codes

401

Unauthorized

402

Payment Required

403

Forbidden

404

Not Found

405

Method Not Allowed

406

Not Acceptable

407

Proxy Authentication Required

408

Request Timeout

409

Conflict

410

Gone

411

Length Required

412

Precondition Failed

413

Content Too Large

414

URI Too Long

415

Unsupported Media Type

416

Range Not Satisfiable

417

Expectation Failed

418

I'm a Teapot

421

Misdirected Request

422

Unprocessable Content

423

Locked

424

Failed Dependency

425

Too Early

426

Upgrade Required

428

Precondition Required

429

Too Many Requests

431

Request Header Fields Too Large

451

Unavailable For Legal Reasons