Show HN: Open-plan-annotator – local annotation UI for working with agent plans

Developer ndom91 released open-plan-annotator, a fully local annotation UI plugin for coding agents including Claude Code, OpenCode, and Pi, that intercepts plan mode and lets users mark up plans with strikethrough, replace, insert, or comment actions before approving or requesting changes. The plugin runs an ephemeral HTTP server and React UI in the browser, sending structured feedback back to the agent for iterative revision, and is available via package managers for each agent harness.

A fully local agentic coding plugin that intercepts plan mode and opens an annotation UI in your browser. Mark up the plan, send structured feedback to the agent, and receive a revised version — iterate as many times as you need until you're ready to approve. Select text to strikethrough , replace , insert , or comment — then approve the plan or request changes - Your coding agent Claude Code, OpenCode, and pi finishes writing a plan - The plugin launches an ephemeral HTTP server and opens a React UI in your browser - You review the plan and annotate it — strikethrough, replace, insert, or comment on any section Approve to let the agent proceed, or Request Changes to send your annotations back as structured feedback- The agent revises the plan and the cycle repeats until you're satisfied Everything runs locally. open-plan-annotator is package-managed as a plugin within your harness of choice. The main plugin package then installs the specific local platform runtime it needs for your host linux / darwin , x86 64 / arm64 , etc . After installing the plugin, your agent will call open-plan-annotator autonomously when you ask it to "make a plan" or any similar such comment, including in claude-code specifically as a hook when exiting PlanMode . Alternatively, you can call it yourself explicitly via the exposed command. See below for more details. Install from inside Claude Code: /plugin marketplace add ndom91/open-plan-annotator /plugin install open-plan-annotator@ndom91-open-plan-annotator What you get: ExitPlanMode hook: opens the annotation UI whenever Claude submits a plan /annotate-plan task description : asks Claude to draft a plan and send it to the UI open-plan-annotator : runtime command invoked by the hook Third-party marketplace auto-update is disabled by default in Claude Code. Enable auto-update for the ndom91-open-plan-annotator marketplace in the Marketplace UI if you want updates automatically. Add the plugin to your OpenCode config opencode.json or .opencode/config.json : { "plugin": "open-plan-annotator@1.8.7" } What you get: annotate plan : tool the agent calls after drafting a markdown plan open-plan-annotator : runtime command spawned by the plugin- optional implementation-agent handoff after approval Restart OpenCode after installing or updating so it reloads the package-managed runtime. Install the Pi extension: pi install npm:@open-plan-annotator/pi-extension What you get: annotate plan : tool the agent calls after drafting a markdown plan /annotate-plan plan markdown : command for manually reviewing supplied text or the latest assistant message open-plan-annotator : runtime command used by the extension Manual review examples: /annotate-plan /annotate-plan Plan\n\n1. Do the thing Install globally if you want to run the CLI directly: bun add -g open-plan-annotator npm install -g open-plan-annotator This adds the open-plan-annotator command. To verify the resolved runtime: open-plan-annotator doctor You can also review a Markdown plan directly from disk, which is useful for agents without a native plugin: open-plan-annotator review /absolute/path/to/plan.md The command opens the same local review UI and blocks until approval or requested changes. It prints review result JSON to stdout when the user is done. Generic agent setup instructions are available with: open-plan-annotator agent-setup open-plan-annotator help agent Claude Code : navigate to the /plugin - "Installed" - open-plan-annotator entry and select "Update", then restart Claude Code. OpenCode : bump the version number in your opencode.jsonc plugins open-plan-annotator entry, then restart OpenCode. Pi : update the Pi extension, then restart Pi. Manual/global install : update the npm package, then rerun open-plan-annotator . | Action | Shortcut | Description | |---|---|---| | Delete | d | Strikethrough selected text | | Replace | r | Replace selected text with new content | | Insert | s | Insert text after the selection | | Comment | c | Attach a comment to selected text | | Approve | Cmd+Enter | Approve the plan and proceed | | Request Changes | Cmd+Shift+Enter | Send annotations back to the agent | bun run dev Starts the Bun server on port 3847 with a test plan and the Vite dev server on port 5173 with HMR. bun run lint check bun run lint:fix auto-fix bun run format format - Architecture: docs/architecture.md - Operations: docs/operations.md - Release process: docs/release.md MIT