agentDefinitions
A Claude Code settings key, read out of the shipped bundle. It was in the build from v2.1.315 and was gone by v2.1.317.
Session telemetry now records whether todo tools were enabled for you.
Not Anthropic's. This is the line from the earliest changelog entry here that named it, v2.1.233.
In the changelogs
4Releases whose published page names agentDefinitions.
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v2.1.269
Session/tool-use context object grows a large set of new accessors
The internal per-session context object gained many new fields covering effort, hooks, tools, and skills
found in this entry's text
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v2.1.236
Agent, MCP and UI caches scoped per session
Agent, MCP and interface caches now die with the session instead of lingering in the process.
found in this entry's text
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v2.1.235
App render root and transcript view reworked; process-global singletons moved behind accessors
Render root and transcript view reworked; several process-global singletons became per-instance state
found in this entry's text
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v2.1.233
Session telemetry records whether todo tools were on
Session telemetry now records whether todo tools were enabled for you.
found in this entry's text
First cited
1The earliest release whose published evidence quoted agentDefinitions was v2.1.236, 19 Aug 2026. That is the oldest release this project wrote about it, so it is a floor on the name's age and not the release that introduced it. It is not a presence reading: which builds carried the name is the table below.
Presence across releases
2Build by build
5One row per release since the first build this name was read out of. Absent means the build was read and the name was not in it, never mined means no bundle for that release was ever archived, and a declared type or a default is only ever what that release's own bundle stated.
Read out of the published npm bundle release by release, and out of Anthropic's own documentation as this site captured it. Nothing on this page is a description anybody here wrote about what the settings key does. All settings keys.