Unclear It is not clear when this limit applies, since an unidentified check decides whether the old unlimited reading is used instead.
What
A background hook is a command of your own that Claude Code runs without waiting on it. Hooks can print JSON, a structured text format, as their answer. Claude Code now limits how many keys it will read from that output in total, and how deeply it may nest. Output past either limit is not read. Claude Code logs an error asking the hook to print one answer with fewer keys. An answer with an empty payload is now treated as empty.
Why
Very large hook output could otherwise slow Claude Code down or swamp it. If you write hooks, keep their JSON answers small.
Something disagreesSomething we can check disagrees with this entry, or the writer said they could not settle it.
The writer flagged doubt
It is not clear when this limit applies, since an unidentified check decides whether the old unlimited reading is used instead.