content[0].text is undefined when the model returns a thinking block first

Cannot read properties of undefined

Verified 2026-07-18 · Confirmed by 0 builders · Trust 50/100

Cause

Models with adaptive thinking can put a thinking block before the text block. Whether they do depends on the prompt, so short tests return text first and look fine.

Fix

Collect every block whose type is text and join them; fail loudly when there is none. Test with the real payload, not a toy prompt.

Apply

const text = res.content.filter(b => b.type === 'text').map(b => b.text).join(''); if (!text) throw new Error('no text block, stop_reason=' + res.stop_reason);

Affects: Claude models with adaptive thinking, July 2026

Have your agent know this before it fails

claude mcp add --transport http footgun https://getfootgun.com/api/mcp