I started this in January as a hook for Claude Code's plan mode: when it finished planning, instead of approving a wall of text in the terminal, the plan opens in your browser and you could mark it up like a document. Your annotations go back into the agent session.

It grew from there. There's now PR-style code review (git, jj, p4, GitHub/GitLab PRs) and annotation for markdown, URLs, and folders. Agents produce a lot of HTML now, so Plannotator renders those artifacts and lets you annotate them too. Nine harnesses are supported: Claude Code, Codex, Copilot CLI, Gemini, OpenCode, Kiro, Droid, Amp, and Pi. Over 100 contributors.

Nothing leaves your machine unless you share... which is E2E encrypted: eg. the plan is encrypted in the browser, the server stores ciphertext, and the key lives in the URL fragment.

As agents get better, the bottleneck shifts to review before and after agents work (obvious to us all now).

Open source, MIT or Apache-2.