define-word

A Claude Code mod for looking up words without leaving the terminal.

• Select a word (or a phrase of up to three words) with the mouse, and a toast shows a short definition in the top-right corner. The status line says what it's looking up while it works.
• /define (or /define <word>) opens a side pane with the full dictionary entry and a short explanation of what the term means in the current conversation.

Nothing it shows is added to the conversation; Claude never sees it.

Requirements

• Claude Code 2.1.287 or later (mods). Tested with 2.1.288; the mods API can change between releases.
• The fullscreen layout, "tui": "fullscreen" in ~/.claude/settings.json. On the main-screen layout the terminal owns the mouse selection, so the toast never fires; /define <word> still works.

Install

claude plugin marketplace add brianium/define-word
claude plugin install define-word@brianium

Update with claude plugin update define-word@brianium.

What it sends where, and what it costs

A mod runs with your permissions, so here is everything this one reaches:

| When | Where it goes | Cost | |---|---|---| | You select a term | The term, to the free dictionary at api.dictionaryapi.dev | Free | | The dictionary lacks the term or is slow (> 0.7 s) | The term, to Haiku on your plan or API key | One small completion | | You run /define | One extra question over this conversation, on your main model, with every tool denied | Mostly a prompt-cache read, plus a few sentences of output | | You run /define in a resumed session before its first new turn | The text of the latest messages (up to about 24,000 characters, tool calls left out), to Haiku | One small completion |

Lookups are cached for the session. Run claude plugin validate . in this repository to list every hook and call the mod makes.

How it works

Claude Code has no event for a mouse selection, so the mod checks $.ui.selection() every 150 ms and looks a term up once the same selection has held for two checks, so a drag in progress doesn't fire on half a word. Multi-line selections, anything over three words, and anything that looks like code (paths, flags, env_vars, camelCase, name@scope, words with digits) are ignored, so selecting text to copy stays quiet. /define <word> looks up whatever you type.

/define opens the pane at once and fills its two sections as they arrive: the dictionary entry (the same lookup as the toast), and the in-conversation meaning, from $.model.fork, which asks the main model one question over the conversation as last sent without adding it to the transcript.

A fork can only replay a request this process has already sent, so right after --resume (before your first new turn) it has nothing to fork. The mod then reads the transcript with $.session.messages() and asks Haiku the same question over the newest messages; the pane notes when Haiku answered.

Development

claude --plugin-dir ~/Projects/define-word   # load for one session, hot-reloading
claude plugin test                            # run tests/ with no session or network
claude plugin validate --strict .             # check the manifest and module

Claude Code writes type declarations for your build to .claude-plugin/types/ on every load (ignored by git), so tsc -p . type-checks once the mod has loaded once.

To release, bump version in .claude-plugin/plugin.json and push; users on the same version won't see new commits.

License

MIT. See LICENSE.