aside

A read-only side chat for Claude Code, as a mod (a plugin built on function hooks).

/aside opens a pane beside the transcript. You ask questions about the session so far; a tool-less fork of the session's own transcript answers, sharing the main thread's prompt cache. Nothing is written back into the main thread: the model in the main session never sees your side questions or their answers, and the side chat cannot call tools, edit files, or submit prompts.

┌ transcript ─────────────────────────┬ aside ──────────────────────────────────┐
│ ❯ refactor the auth middleware      │ 2 questions                              │
│ ● Reading src/auth/*.ts ...         │ you: which files has it touched so far?  │
│   Edit(src/auth/session.ts)         │ aside: src/auth/session.ts and           │
│   ...                               │ src/auth/index.ts; tests are untouched.  │
│                                     │ fork · 1244 ms · read 72848 · new 242    │
│                                     │                                          │
│                                     │ you: is it planning to change the tests? │
│                                     │ aside: thinking…                         │
│                                     │ > _                                      │
│                                     │ [ Clear ] [ Close ]                      │
└─────────────────────────────────────┴──────────────────────────────────────────┘

Requirements

• Claude Code 2.1.270 or newer with function hooks enabled: CLAUDE_CODE_ENABLE_FUNCTION_HOOKS=1. Without the flag the module is not loaded and /aside does not exist. Function hooks are early access and the API changes between releases; this mod is validated and tested against 2.1.270 (see docs/investigation/).
• A terminal at least 110 columns wide for the pane to dock beside the transcript; narrower, it opens inline above the prompt.

Install

From the marketplace in this repository:

/plugin marketplace add JayDoubleu/aside
/plugin install aside@aside

Or straight from a checkout:

git clone https://github.com/JayDoubleu/aside
CLAUDE_CODE_ENABLE_FUNCTION_HOOKS=1 claude --plugin-dir ./aside

Use

| | | |---|---| | /aside | open the pane | | /aside what has changed so far? | open it and ask | | Tab | put the cursor in the pane's input (the pane opens focused, but the cursor is not in the field yet on 2.1.270) | | Enter | ask | | Esc | give the keys back to the composer | | ctrl+x tab | focus the pane again | | ctrl+x x | close the pane |

Every answer's footer says where it came from and what it cost:

• fork · 1244 ms · read 72848 · new 242 · out 100: a fork over the transcript. read is the prompt-cache read of the whole session prefix, billed at the cache-read rate; new is what was added; out the reply.
• live · 800 ms · 5120 chars of transcript sent uncached: asked before the session's first turn had completed, when there is no transcript snapshot to fork yet, so the question was answered by a plain completion over the transcript's text (see liveFallback).

Asked while a later turn is running, a fork answers from the last completed turn: you get the state as of Claude's previous reply, not the half-finished one.

Options

Set under /config or in settings.json as pluginConfigs["aside@aside"].options:

| option | default | | |---|---|---| | liveFallback | true | When no turn has completed yet (the session's first turn): on answers at once through $.model.complete over $.session.messages() (uncached, capped at 60,000 characters of transcript, marked live); off queues the question and a fork answers it when the turn ends. | | liveModel | haiku | Model for live answers (a --model value). Forks always use the session's model. | | maxHistory | 8 | Earlier side exchanges carried in each question's prompt. |

What "read-only" means here

claude plugin validate . --strict prints the module's complete static surface:

hooks: session.start, command.run{command=aside}, turn.complete, ui.render{component=Pane}, ui.input{plugin=aside, element=q}, ui.press{plugin=aside}
calls: $.clock.now, $.command.register, $.model.complete, $.model.fork, $.session.messages, $.ui.close, $.ui.invalidate, $.ui.open, $.ui.resolve

No fs, process, http, store, tool or prompt verbs, so the module cannot reach the working tree, the network, or the main thread's prompt. The engine's fork denies every tool call and never writes to the transcript. The /aside command answers {} (a { text } answer would become transcript messages the model reads). An organization can refuse the module on that listing in a plugin.register hook.

Cost

A fork costs one prompt-cache read of the whole session prefix plus a few dozen new tokens: measured at 72,848 cache-read tokens on a 73k-token session, about $0.008 on Haiku and proportionally more on the session's model. Right after /compact the summary goes in uncached (~3k tokens). Live answers send the transcript text as fresh input to liveModel.

Development

npm run validate     # claude plugin validate, offline, no API key
npm test             # node --test, no API key
npm run eval         # claude plugin eval: real sessions, needs credentials, spends a few cents

The eval (evals/) checks the mod is invisible to the model: a trivial prompt gets the same reply with and without the plugin loaded. It passed 2/2 runs on each arm on 2.1.270 (docs/investigation/evidence/eval-invisible-to-the-model.json).

Tests run on Node 22's native TypeScript support against a small fake engine (tests/harness.ts) that dispatches events through the registered hooks the way Claude Code does. claude plugin test is 2.1.271+ and not used yet.

Typing: run /plugin-types in a session to write .claude/types/claude-code.d.ts next to tsconfig.json.

docs/investigation/ holds the measurements this design rests on: FINDINGS.md (nine questions, each answered with debug-log lines and rendered screens), DESIGN.md, the throwaway probe plugins, and the evidence.

License

MIT