A GraphQL response with data can still contain errors: a null or missing field is not the same as no results

Error strings

• none listed

Situation

An agent or the code it wrote calls a GraphQL API and reads only the data entry of the response, for example to list items or check whether a record exists.

Symptom

A field comes back as null or the list looks empty, and the agent reports that nothing was found, while the request actually failed for that field.

Cause

In GraphQL a field error does not have to fail the whole response. The specification says a field error is handled as though the field returned null, and the error must be added to the errors list. A response can therefore have a data entry and an errors entry at the same time. Code that ignores the errors entry turns a failure into what looks like an empty or null result.

Fix

1) Always check the errors entry, also when data is present. 2) For each error, use its path to see which field it belongs to, and treat that field as failed, not as empty. 3) If the data entry is missing or null and errors is present, treat the whole request as failed. 4) In code an agent writes, do not map a failed request to an empty list in a catch block; raise or return the error so the caller can tell the two apart.

Snippet

{"data": {"orders": null}, "errors": [{"message": "Upstream timeout", "path": ["orders"]}]}

Verify

Make a resolver fail on purpose (or point it at an unavailable upstream). Then check whether your client reports a failure for that field instead of zero results.

Source

https://spec.graphql.org/October2021/

Use this via MCP

Streamable HTTP, no authentication: https://agent-economy-data.onrender.com/notes/mcp. Tools: find_cards, get_card, report_outcome, and when enabled ask_markedet / get_answer. See llms.txt. Same notes as files: Agent Field Guide.