Whiteboard

// Overview

Whiteboard is an open-source desktop app, built by the Y Combinator W26 startup /dev/fast, where humans and coding agents architect software together in a shared workspace. It does not replace your coding agent. It plugs into the ones you already use, such as Claude Code and Codex, and gives the agent an SDK to draw on an in-app canvas that explains its work: sequence diagrams, entity-relationship diagrams and other architecture-level views.

Every element on the canvas links back to the code behind it. The app vendors Code OSS as its editor, so navigation uses VS Code keybindings and LSP support. Next to the diagrams sits a semantic diff viewer written in Rust: it compares code by its syntax tree, can show long functions as pseudocode, always shows function signatures, and folds tests and documentation by default so the reviewer starts with the parts that matter.

A Decision Log lets agents query and link their own traces, so a reviewer can see the requirements, the implementation choices and the decisions the agent made on its own, and check whether they make sense. Whiteboard runs locally against your repositories on macOS and Fedora Linux and is MIT-licensed. It sends anonymous telemetry that excludes code, diffs, prompts and model output, and it can be switched off. The README lists current limits: no file editing inside the app, one repository per review, and shared reviews that do not update across machines.

// What it does

• Agent SDK that lets Claude Code, Codex and other agents draw on an in-app canvas to describe their work
• Sequence diagrams and entity-relationship diagrams that link each element to the underlying code
• Code OSS editor with VS Code keybindings and LSP navigation
• AST-aware semantic diff viewer in Rust that can show long functions as pseudocode and folds tests and docs by default
• Decision Log for auditing the requirements, implementation choices and autonomous decisions in an agent's trajectory
• Runs locally against your repositories; telemetry excludes code, diffs, prompts and model output and can be disabled

// Getting started

Whiteboard is a desktop app for macOS and Fedora Linux. Install it from the project's download links, then ask the coding agent you already use to write a Whiteboard review of its change.

https://install.dev.fast
https://install.dev.fast/linux

Commands and code are distilled from the project's own documentation — always check the official repo for the latest.

// When to use it

• Reach for it when an agent's change is too large to read line by line and you want to check the architecture first
• Reach for it when reviewing spec-level or data-model changes, where a sequence or ER diagram says more than a diff
• Reach for it when you need to audit which decisions an agent made on its own during a long run
• Reach for it when you want a diff that hides noise like tests and docs and shows long functions as pseudocode

// How Whiteboard compares

Whiteboard alongside other open-source ai code review & security tools AI/TLDR tracks, ranked by GitHub stars.