Subcanvas

Whiteboards inside whiteboards, with notes in every box

Productivity

Open Source

Developer Tools

GitHub

Visit WebsiteSee on Product HuntGithub ⧉

Hi everyone, I built Subcanvas because I wanted a place to quickly explain a system's architecture in engineering meetings, and a place to write down ideas and concepts that need several layers of abstraction to make sense. Most architecture diagrams I see in meetings stop at one level. The box that says "Payments" never tells you what's inside Payments, and the arrow between two services never tells you what goes over it. In Subcanvas every box and every arrow can hold something: a whole whiteboard of its own, or a page of notes. Double-click a box to go inside it, and the breadcrumb at the top takes you back out. You can try it without an account, on an example software project (https://subcanvas.app/try) or on a course laid out as notes (https://subcanvas.app/try/produc...). The part to try first is Import from GitHub. Paste a public repository and you get a box for each main folder, with its README inside, and folders inside folders as whiteboards inside boxes. Connect GitHub in Settings and it imports your private repositories too, read-only. The arrows come from `.subcanvas` files: a few lines of YAML in a folder that say what it talks to and how. Most repositories don't have them yet, so you'll start with the boxes and draw the arrows yourself, or add the files. Either way the diagram is yours to move, delete from, and draw on. That is the difference from tools like GitDiagram, which draw the whole picture for you: here the import is a starting point you edit by hand, and every box and arrow can open into its own whiteboard or page. A public diagram also embeds in a README as a picture that follows your edits in Subcanvas within minutes and links to the live version. The import itself is a one-time copy, so later commits don't change it. The Subcanvas README shows its own design this way: https://github.com/subcanvas/sub... Other things that work today: - Live editing with everyone's cursors. - Lock, in a whiteboard's ••• menu, so nothing moves by accident. - Each box and arrow chooses how its page opens: beside the whiteboard, in a pop-up, or as a full page. - An MCP server, so Claude Code, Codex, Cursor, or any other agent can read and edit your whiteboards as you, with your permissions. For Claude Code there's a plugin that also teaches it to nest boxes and put a page behind each arrow. - Any box or arrow can link to the code it stands for, one click away. - Paste Mermaid and get boxes and arrows you can click into. - Import notes from Notion, Obsidian, or a folder of Markdown, pictures included. It's open source under the AGPL-3.0, and you can run your own copy. On subcanvas.app it's free for one person: as many public projects as you like, and up to 100 private whiteboards and pages. Pro is $5 per editor a month once a workspace has a second editor or needs more private work, and viewers are always free. For the Product Hunt community, the code PRODUCTHUNT gives a new workspace 3 months of Pro free, until November 19. I built it with Claude Code, and every change runs database permission tests and end-to-end tests in a real browser before it ships. Sign up free (no card), paste a repository you know well, and tell me what the boxes miss.