What Is HTTP 400 Bad Request?

HTTP 400 Bad Request explained, and what it means when you see it in CI/CD and deployments.

HTTP 400 means the request was malformed and the server refused to process it.

What it means

A 400 points to a client-side mistake: invalid JSON, a missing required field, a bad query parameter, or a malformed header. The fix is in the request, not the server.

When you see it in CI/CD

In CI, a 400 from an API test usually means the test payload is wrong or an env var rendered empty. This is deterministic; retrying will not help.

Key takeaways

• 400 means a malformed request.
• The fix is client-side.
• Retrying does not help a 400.

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