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Mistral API error

Mistral API 400 Bad request: what it means and how to fix it

Error message
400 Bad request

Retry? Not statedLast verified 2 documented fixes2 sources

What it means

The request body is malformed or missing required fields. Requests that exceed the model's context window also return 400 Bad Request.

Causes

  • Invalid JSON syntax
  • Missing the model or messages field
  • Unsupported parameter value (for example temperature outside the 0 to 1 range)
  • Prompt plus max_tokens exceeding the model's context window

How to fix it

  1. Fix 1.

    Check your request body against the API reference and validate JSON before sending.

  2. Fix 2.

    Token counts include both input and output tokens; plan max_tokens so the total fits the model's context window.

More Mistral API errors

All 11 Mistral API errors

HTTP 400 at other providers

Compare 400 across providers

FAQ

What does the Mistral API error "400 Bad request" mean?

The request body is malformed or missing required fields. Requests that exceed the model's context window also return 400 Bad Request.

How do I fix Mistral API "400 Bad request"?

There are 2 documented fixes. Start with the first: Check your request body against the API reference and validate JSON before sending.

Should I retry Mistral API "400 Bad request"?

Not stated. The official docs do not say whether this error is retryable.

Which other AI APIs return HTTP 400?

Per their official error docs: Amazon Bedrock (400 ValidationException; 400 ServiceQuotaExceededException; 400 IncompleteSignature; 400 InvalidAction; 400 NotAuthorized; 400 RequestExpired), Anthropic API (400 invalid_request_error; 400 invalid_request_error (spend limit reached)), Azure OpenAI (400 Bad Request; 400 content_filter), Cohere API (400 Bad Request; 400 Bad Request (too many tokens)), DeepSeek API (400 - Invalid Format), Gemini API (400 invalid_request; 400 failed_precondition; 400 parameter_unknown; 400 INVALID_ARGUMENT; 400 FAILED_PRECONDITION), Groq API (400 Bad Request), OpenAI API (400 invalid_request_error (Invalid service_tier argument); 400 BadRequestError), OpenRouter (400 invalid_request; 400 invalid_prompt; 400 context_length_exceeded; 400 max_tokens_exceeded; 400 token_limit_exceeded; 400 string_too_long; 400 invalid_image; 400 image_too_large; 400 image_too_small; 400 unsupported_image_format; 400 image_download_failed), Vertex AI (400 INVALID_ARGUMENT / FAILED_PRECONDITION), xAI API (400 Bad Request).

Sources

Last verified against 2 sources: Mistral API's official docs and official SDK repositories.

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