diagram-design is an MIT-licensed Claude Code skill with 27 editorial diagram types that emits self-contained HTML, aimed at the per-seat diagramming subscriptions your team renews every year: Visio at $5 to $15 a user per month, Lucidchart at $9 to $10, Miro Business at $20.
The current state architecture diagram in your next client proposal, the swimlane that shows who approves what, the consultant 2x2 that anchors the strategy slide: somebody on your team is dragging boxes around to make those right now, on a seat that bills whether they open the app twice a year or every day. Visio Plan 1 runs $5.00 per user per month and Plan 2 runs $15.00, both paid yearly. Miro is $8 per member per month on Starter and $20 on Business, billed yearly. A Claude Code skill called diagram-design went to the top of GitHub Trending overnight by generating those same diagrams from a paragraph of description, under an MIT license, in HTML files you own outright.
The star delta is the part worth noticing. The repo picked up 1,612 stars in a single day against a base of 6,120. That is roughly a quarter of its entire history arriving in 24 hours, and it is the largest relative move on the trending board today by a distance. Whatever else is true, a lot of people looked at this and immediately understood what it was for.
What it actually is
It is not an app. It is a skill directory: one SKILL.md file plus 27 reference files, one per diagram type, that a coding agent reads before it draws anything. Architecture, flowchart, sequence, state machine, entity relationship, timeline, swimlane, quadrant, tree, org chart, Venn, layer stack, pyramid and funnel, consultant 2x2, radar, loop, current state IT, Gantt, bar, line, scatter, process, medallion, data flow, integration, security matrix. You describe the thing in words. It writes a self-contained HTML file that opens in a browser with no build step, no JavaScript, and no external image files. Playwright handles SVG and PNG export when you need a static asset for a deck.
The interesting engineering is not the drawing, it is the constraint list. The skill hard-codes an opinion: one accent color carrying one or two focal points, a target density around 40 percent, every coordinate divisible by four, hairlines at one pixel, border radius capped at ten pixels, and no drop shadows anywhere. It names its typefaces (Instrument Serif for titles, Geist Sans for labels, Geist Mono for anything technical) and it will pull your brand colors and fonts in, with light, dark, and full editorial variants. That is a style guide expressed as instructions rather than as a template library, which is why the output does not look like the rounded-rectangle sludge you get from asking a model to "make a diagram."
Installing it takes one line if you already run Claude Code. /plugin marketplace add cathrynlavery/diagram-design, then /plugin install diagram-design@diagram-design. Codex users get it through npx skills add. There is also a clone and symlink path into ~/.claude/skills for anyone who wants to read the files before trusting them, which, given that a skill is a set of instructions your agent will follow, is not a bad habit.
Who this is actually for
The clearest fit is the person who owns a diagramming seat and uses it four times a quarter. Solutions consultants and sales engineers producing architecture and integration diagrams for proposals. Internal IT and ops documenting current state before a migration. Product marketing drawing the category diagram that goes in the deck and then in the blog post and then on the website. Founders writing the docs page nobody wants to write.
Run the arithmetic at your own headcount. Forty people on Miro Business at $20 per member per month billed yearly is $9,600 a year. The same forty on Lucidchart Team, which published pricing trackers put at $10 per user per month, with the Individual plan at $9, is $4,800. Most orgs are not paying for forty active diagrammers. They are paying for six people who diagram and thirty four who were provisioned once and never logged back in. That second group is the line item this repo actually threatens.
The honest caveats
Free is doing some work in that sentence. The skill needs a coding agent to drive it, so the real floor is your existing Claude Code or Codex subscription plus Python 3 for the linter and a Playwright install for PNG export. If nobody on the team already lives in a terminal, this is not a swap you make this week.
More importantly, the seat you are paying Lucid or Miro for is not really the drawing. It is the shared canvas, the comment threads, the version history, the shape library your team standardized on, and the Confluence embed that keeps the diagram from going stale. diagram-design replaces none of that. It gives you a file. When a stakeholder wants the box moved, they are either editing markup or asking the agent again, and there is no world where your VP of sales does the first one. There are also no tagged releases yet, six open issues, and a commit history that reads like one person with strong opinions shipping on their own cadence, most recently this morning. That is a real maintenance profile, not a knock, but plan for it.
The thing that will not show up on the invoice is the taste. The reason a decent diagram used to cost either a seat license or a design request was never the rectangles. It was somebody deciding what to leave out. That decision just shipped as 27 markdown files, and it is sitting in a public repo where anyone can read exactly how it was made.