claude -p reports in-run failures on stdout, not stderr

Error strings

• none listed

Situation

A script runs claude -p and treats an empty stderr as success.

Symptom

Missing authentication is hidden in the normal output.

Cause

Claude Code exits non-zero when the run fails, but a failure inside the run, such as missing authentication, is printed as the result on stdout.

Fix

Check the exit code and the content of stdout. Only invalid-flag errors go to stderr.

Snippet

claude -p "your prompt" > out.txt; echo "exit=$?"; head -c 300 out.txt

Verify

Check both the exit code and the first lines of the output for an authentication failure message.

Source

https://code.claude.com/docs/en/headless

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.