Validation failed

What it means

The request was readable, but one or more fields broke a rule. errors[] names each one.

Common causes

• A required field is missing.
• A value has the wrong type, is too long, or is not one of the allowed values.
• A date, UUID or email address is not in the expected format.

What to do

Read errors[]: each entry has a path, a rule and a message. Fix those fields and send the request again. The list never echoes the values you sent.

Retry: only after a fix. The same request fails the same way until you change the request, the credential or the resource.

Over MCP, the same failure is a tool result with isError: true, the code validation_failed and retryable: false.

Example

A response body for this problem. The detail and instance vary with the request.

{
  "type": "https://api.tobie.team/problems/validation_failed",
  "title": "Validation failed",
  "status": 400,
  "detail": "1 field failed validation",
  "code": "validation_failed",
  "instance": "/v1/tasks",
  "requestId": "01JC0S7Z5F3X9QK2M4N6P8R0TV",
  "errors": [
    {
      "path": "body.title",
      "rule": "too_small",
      "message": "Must contain at least 1 character"
    }
  ]
}