Error Handling

Error response format

All errors return a JSON object with an error field:

{
  "error": "Description of what went wrong."
}

Some errors include additional fields for context.

Code	Meaning	When
`200`	Success	Request processed successfully
`400`	Bad Request	Missing or invalid `html` field, invalid `clients` array, empty content
`413`	Payload Too Large	Request body exceeds 1MB
`422`	Unprocessable Entity	JSX or MJML compilation failed
`429`	Too Many Requests	Rate limit or daily quota exceeded
`500`	Internal Server Error	Unexpected server error

{ "error": "Missing or invalid 'html' field. Provide the email HTML, JSX, or MJML as a string." }

{ "error": "Content must not be empty." }

{ "error": "Content exceeds 500KB limit." }

{ "error": "'clients' must be an array of client ID strings." }

When format is "jsx" or "mjml" and compilation fails:

{
  "error": "Failed to compile React Email component.",
  "phase": "transform"
}

The phase field indicates where compilation failed (transform or render).

See Rate Limiting for details.

The API enforces a 1MB hard limit on request body size and a 500KB limit on the html field content.