Mods - a plugin can now watch your session (Claude Code 2.1.287)Capability

Claude Code 2.1.287 added mods: a plugin can now change what the terminal shows and does, and one built-in mod puts a side agent on your session to flag what you and Claude miss. Ten minutes to switch it on and watch one note arrive.

Until now a plugin could add three kinds of thing: skills (instructions Claude reads), hooks (scripts that run at events such as a tool call), and MCP servers (tools). A mod is a fourth kind: TypeScript that runs inside Claude Code itself. It can draw a pane, a band above the prompt, a status line or a toast; it can intercept what a tool is about to do; it can replace a feature. Mods ship inside plugins, hot-reload while you work, and your skills list already carries the authoring skill for them (plugin-authoring: 'Make a mod: a live pane, band, status line, toast or hook').

'You should know' is the first built-in mod. A second, smaller agent reads your session alongside the main one and posts short notes when something looks off: a file about to be overwritten, a claim that was not verified, a risk nobody mentioned. It flags; it never blocks, edits or approves. Two limits matter for you: it runs only in first-party interactive sessions with telemetry on (so your headless plan-day, nightly and weekly runs never see it), and its tokens land on the same usage meter those headless jobs share — the meter that capped out on 9-11.

The bloat axis the weekly review weighs: a skill costs context every turn, a hook costs a script run every event, and a mod costs runtime for as long as it is enabled. That is why the 10-4 doc frames it as a one-week trial with a named off switch, not an install.

Worked example

Three commands: confirm the version, see what is installed, and turn the watcher on inside a session.

claude --version                 # 2.1.289 today; mods arrived in 2.1.287
claude plugin list | head -25    # what is installed and enabled right now

# inside an interactive session (not claude -p):
/plugin enable cc-plugin-you-should-know@builtin
# ... do one small real task, read any 'You should know' note ...
/plugin disable cc-plugin-you-should-know@builtin   # the off switch

• The version line is the gate: anything below 2.1.287 has no mods and the enable command will say so.
• The plugin list shows your local-plugins marketplace (superpowers@tom-local) next to the official ones; the watcher will appear here once enabled.
• The slash command works only inside a session you are sitting in. A headless run cannot enable it (2.1.285 made the same rule for auto-memory), which is the right default for a thing that spends tokens.
• The disable line is the whole rollback. Nothing is written to CLAUDE.md or settings.json by hand.

Gotchas

• Telemetry off or a third-party provider means the watcher silently does nothing. Your interactive sessions are first-party, so it should run.
• It is not a security control. It noticed nothing on 10-1 because it did not exist; it would have flagged, not prevented.
• A third-party mod runs with the session's full permissions — the skill-addition rule (read SKILL.md and every script before install) applies harder here. Built-in means Anthropic wrote it.
• Your headless wrappers pass --settings '{"enabledPlugins":{}}'; even if you enable the watcher, the nightly and plan-day runs are unaffected either way.