venn-diagram-generator
中文說明 · Live: https://venn.applepig.net
A single-page WYSIWYG Venn diagram generator. Pick 2, 3 or 4 circles (extra shapes such as rows and 5–6 circle flowers live in a dropdown next to them), give the picture a title, click any region on the canvas to type, tune font sizes, recolour individual regions, then download a PNG you can paste anywhere. The whole editor state is compressed into the URL's s parameter, so a share link is the picture: paste it into a chat app and og:image renders a preview. No login, no account, stateless server. UI available in Traditional Chinese, English and Japanese, picked from the language dropdown in the panel (remembered in the venn.lang cookie), ?lang=, or Accept-Language.
Architecture
SVG is the single source of truth for rendering. engine/render-svg.ts exposes a pure renderSvg(state, options); the browser drops its output straight into the DOM as a live preview, and the server hands the very same output to @resvg/resvg-js to get a PNG — what you preview is what you download. Text layout never measures the DOM: widths are estimated from character classes (CJK 1em, other 0.62em, whitespace 0.3em) so front end and back end lay out identically.
engine/ types, defaults, shapes/ (ring & row registry), layout, region-geometry,
render-svg, state-codec — pure geometry, layout and codec, zero product copy
content/ palette, templates/, strings/, locale, state-presets — default memes and UI strings
ui/ Vite + vanilla TS editor
server/ Hono: static HTML/API docs, OpenAPI, SVG/PNG/OG endpoints, meta injection for GET /
cli/ the `venn` command: spec (letters <-> masks), flags (merging), venn (I/O shell)
skills/ Claude Code skill shipped by the plugin in .claude-plugin/
deploy/ Dockerfile, compose.yml, compose.dev.yml, deploy.sh
Circle positions are always derived from arr / n / overlap / radius — coordinates are never stored. ring(n) keeps a frozen angle table per circle count so links shared by older versions keep rendering byte-for-byte identically.
URL state format
?s= holds base64url(deflate-raw(JSON)). The browser uses CompressionStream('deflate-raw'), Node uses zlib.deflateRawSync — same format both ways. Anything that fails to inflate or does not match the schema is a 400.
{
"v": 1, // state version, must be 1
"arr": "row", // "ring" | "row"; omitted means "ring"
"n": 2, // circle count: ring 2–6, row 3–6
"title": "My diagram", // image title, drawn in a band above the diagram;
// omitted or empty means no title (same 80-char cap as a slot)
"title_fill": "#e04848", // title text colour; omitted means automatic black or white.
// Never encoded when there is no title
"style": "flat", // translucent | flat | outline
"stroke_width": 0.01, // circle outline width as a fraction of canvas width, 0–0.03;
// omitted means the style default (0.006 for outline, 0 otherwise)
"stroke": "#ff0000", // outline colour; omitted means #000000.
// Never encoded when the resolved width is 0
"opacity": 0.6, // 0–1, only used by translucent: a region is its members'
// colours mixed like paint, then laid over the background
// at this opacity, so circle order never changes a colour
"overlap": 1.2, // centre distance / r, 0.6–1.6
"radius": 0.3, // circle radius as a fraction of canvas width
// (ring 0.2–0.35, row 0.1–0.35)
"colors": ["#2e9be6", "#e6a92e"], // length must equal n
"bg": "#fafafa",
"size": 1200, // integer, 400–2000
"texts": { // key is the member-circle bitmask, as a decimal string
"1": { "t": "My duty" }, // circle i = bit i, so 3 = circle 0 ∩ circle 1
"2": { "t": "My passion" },
"3": { "t": "Do it\nlater", "fs": 0.09 }
}
}
fs (font size, fraction of canvas width) and fill (per-region colour override, flat only) exist only once the user has adjusted them; absent means automatic. Region text is always drawn at the centre of its region box. Each text slot is capped at 80 characters. Older links may still carry dx / dy text offsets; those are ignored rather than rejected, so the link keeps working.
With a title, the top 18% of the canvas becomes a title band and the diagram (circles and every region text) is scaled down by the same factor, centred horizontally and pushed to the bottom edge — so the output stays square and nothing overflows. Without a title the layout is untouched, byte for byte. The title font size is fitted automatically, manual \n and automatic wrapping both work, and the colour flips between black and white with the background's luminance unless title_fill pins it. A manual title_fs makes the band grow with the text instead — as tall as its lines need, up to half the canvas, beyond which the font size is clamped again so the title never overflows. On a share page the title also becomes the og:title and <title>.
A large radius combined with a large overlap can push the circles past the canvas edge — most easily on ring(5) / ring(6) and the rows. When that happens the whole diagram (circles, every region text, and the title transform already applied) is scaled down about the canvas centre and nudged back inside, leaving a margin of half the outline width — and never less than 0.3% of the canvas width — so the stroke is not clipped either. It only ever shrinks, never enlarges: geometry that already fits comes out byte for byte identical. Layout still runs on the untransformed geometry, so which slots exist and where their text sits are unaffected — the fit is applied at the very end, on top of the title transform.
Which slots a shape offers is derived from its default geometry (a region gets a slot when it has a non-null inscribed box): 3 slots for 2 circles, 7 for a three-circle ring, 13 for the 2×2 four-circle petal arrangement (4 singles + 4 adjacent pairs + 4 triples + 1 centre; the diagonal pairs have no region at the default overlap). A row is a chain rather than a ring, so only neighbours ever overlap and row(3) has 5 slots, not 7 — ring(2) and ring(3) are the only combinations carrying every possible one. Rings of 5–6 and all rows only ship single-circle labels by default. The shape dropdown lists row(3), row(4), ring(5) and ring(6); row(5) and row(6) stay decodable so older links keep working, and the menu adds the current one as a temporary entry when you open such a link.
Without s the editor starts empty: every shape ships a default template (in the current UI language), but it is only shown as a placeholder — in the text fields and, faintly, on the canvas preview itself (renderSvg's ghosts option, which only the editor canvas passes). Nothing is written into the state, so you never have to clear a sample before typing your own, and no download, /api/png or og:image ever contains the ghost text. Switching shape while nothing is typed also switches to that template's style; once you have typed something, your text and style are kept. The og:image for the bare home page still renders the 2-circle template, so the social card is not an empty diagram.
API
GET /api/venn.svg generates an inline SVG from a single URL. Friendly mode takes optional a (A only), b (B only), ab (A∩B), colorA and colorB (#rrggbb). It always uses two circles with product defaults; omitted/empty text is blank, omitted colors use defaults, and empty colors are invalid. No query produces an empty diagram without template/ghost text. Use URLSearchParams or percent encoding: # is %23, + is %2B.
const query = new URLSearchParams({
a: '藥品濫用', b: '物質濫用', ab: '毒品',
colorA: '#E76F51', colorB: '#2A9D8F',
});
const url = `https://venn.applepig.net/api/venn.svg?${query}`;
For all supported styles and shapes, use GET /api/venn.svg?s=<state> with the existing encoded state. These modes are mutually exclusive: unknown/duplicate query parameters or mixing s with friendly fields returns 400 JSON with no-store. Text uses the existing 80-code-point limit, s has the same 7300-character limit, and serialized query length (including ?) is capped at 22156 characters. Successful responses are image/svg+xml; charset=utf-8 with X-Venn-Url for the same editable state. SVG serialization uses the shared renderer without PNG rasterizer workers. Friendly mode is no-cache because defaults can change; s mode preserves the existing immutable one-year cache policy (renderer/watermark changes still need cache invalidation). Fonts are not embedded: standalone readers may display different glyphs, so use PNG when fixed font rendering matters.
The homepage exposes a real API documentation link in its initial HTML. GET /api is a complete English HTML reference with executable examples; no JavaScript is needed. GET /openapi.json returns an OpenAPI 3.1 description (application/vnd.oai.openapi+json), declared by rel="service-desc" links in the homepage head and body. /llms.txt links to both. The specification's per-shape text keys and circle/geometry constraints come from the same shape registry as the validator. Fixed introduction text uses the existing three-language server localization; this needs no SSG framework. Share-specific meta remains dynamic in Hono.
GET /api/png?s=<state> returns image/png sized to state.size, with Cache-Control: public, max-age=31536000, immutable (the parameter is the content). A missing, undecodable or invalid s returns a 400 JSON body { "error": "..." }. API error messages are always English — it is a machine interface and does not follow the UI language.
POST /api/png takes the same diagram as a raw VennState JSON body, so a caller does not have to deflate and base64url a state itself. The response is the PNG plus an X-Venn-Url header holding the editable share link for that diagram. Same validation and the same concurrency limit as the GET; a body that is not JSON, a state that fails validation, or a body over 32 KB return 400 / 400 / 413 as JSON.
The trade-off is caching. GET /api/png?s= is content-addressed and served immutable, so a repeated diagram never re-rasterizes; a POST cannot be cached and is answered Cache-Control: no-store, meaning every request pays for a render. Use POST to produce a diagram, then hand out the s from X-Venn-Url for anything that will be fetched more than once.
GET /api/og.png?v=<n>&s=<state>&lang=<zh-TW|en|ja> is the 1200 × 630 social banner: the branded base image with the diagram composited on top. Without s it renders the home-page sample; lang only comes from the query string (never Accept-Language) so a cached URL cannot be poisoned by whichever crawler arrives first. v is the layout cache version, bumped when the base image or composition changes. Invalid s returns 400 JSON with Cache-Control: no-store.
The home page ships a pre-baked static OG image (pnpm build writes dist/og-default-<hash>.png); share pages point og:image at /api/og.png with their own s.
GET /llms.txt is this section boiled down for an agent that arrives at the site instead of the repo — the endpoints as absolute URLs, the required state fields, the bitmask key convention, and the CLI and plugin one-liners. It is generated from the same origin logic as robots.txt, so a fork serves its own hostname. Change the API contract and it changes here too.
# Build a state with Node, or just copy a link out of the editor
S=$(pnpm exec tsx -e "
import { encodeState } from './engine/state-codec-node';
import { sampleState } from './content/state-presets';
process.stdout.write(encodeState(sampleState()));")
curl -o venn.png "http://localhost:3000/api/png?s=$S"
curl -o og.png "http://localhost:3000/api/og.png?v=6&s=$S&lang=en"
# Or skip the encoding step and POST the state itself
curl -sD headers.txt -o venn.png -H 'content-type: application/json' \
--data '{"v":1,"n":2,"style":"translucent","opacity":0.6,"overlap":1,"radius":0.26,
"colors":["#4285f4","#ea4335"],"bg":"#ffffff","size":1200,
"texts":{"3":{"t":"No sleep"}}}' \
http://localhost:3000/api/png
grep -i x-venn-url headers.txt
Command line
npx -y venn-diagram-generator@1 png --set A=Fast --set B=Cheap --set C=Good \
--text ABC="Pick two" -o pick-two.png
Nothing is fetched at render time: the fonts ship inside the package and @resvg/resvg-js rasterizes locally. Four subcommands — url prints the share link, svg and png write a file, decode <url-or-s> prints the JSON behind an existing link (--raw prints the VennState documented above instead of the friendly format). svg and png print two lines: the absolute path with its pixel size, then the share URL for the same picture.
The CLI never asks you to write a bitmask. Circles are letters (A is the first circle, up to F) and a text slot is named by the set of circles it belongs to, so AB is the overlap of the first two. Letter case and order do not matter, ba is AB. Which slots exist depends on the arrangement: four circles in a ring means A and D never touch, so AD is rejected — and the error lists every legal slot for that combination.
The whole spec can arrive as JSON instead, which is the only sane way to pass CJK text, apostrophes and newlines through a shell. --json takes either format and tells them apart by which key is present — sets means the friendly spec, v means a raw VennState, the exact object the URL carries and decode --raw prints. An object with both or neither is rejected rather than guessed at, and so is a misspelt top-level field — "text" for "texts" would otherwise silently produce a diagram with the overlaps missing.
cat <<'EOF' | npx -y venn-diagram-generator@1 png --json - -o life.png
{
"sets": ["工作", "生活", "睡眠"],
"texts": { "AB": "沒有睡眠", "ABC": "都想要" },
"title": "選三個",
"style": "flat"
}
EOF
Every state field has a flag, so nothing is JSON-only. --arr, --style, --title, --title-fill, --title-fs, --size, --bg, --opacity, --overlap, --radius, --stroke-width, --stroke and --colors '#aabbcc,#ddeeff' map to the fields documented above, and the per-slot ones take the same letter keys: --fs AB=0.09 and --fill AB=#ffffff. All of them override whatever --json supplied, and --set / --text replace only the text, leaving that slot's existing size and fill alone — --text AB= clears the words without discarding the region's colour.
The share link's host comes from --base-url, then VENN_BASE_URL, then https://venn.applepig.net. Exit codes: 0 success, 1 bad arguments or an invalid spec, 2 rasterization failed.
decode round-trips exactly, including manual font sizes and region colours, so you can paste a link from the editor, edit one label in JSON and re-render everything else untouched.
npx -y venn-diagram-generator@1 decode 'https://venn.applepig.net/?s=...' > spec.json
npx -y venn-diagram-generator@1 png --json spec.json -o updated.png
Claude Code plugin
This repo is also a Claude Code plugin, so Claude can draw a real diagram instead of guessing at hand-written SVG.
/plugin marketplace add applepig/venn-diagram-generator
/plugin install venn@venn-diagram-generator
The skill teaches the CLI, carries the table of legal slots for every arrangement, and tells Claude to hand back both the PNG and the editable share URL. Then just ask for a Venn diagram.
Local development
pnpm install
pnpm dev # Hono on 3000; Vite runs in middlewareMode on the same port (HMR included)
pnpm test # Vitest
pnpm typecheck # tsc --noEmit
pnpm build # ui → dist/, baked OG image → dist/, server → dist-server/
pnpm start # run the built server, single port 3000
Two fonts live in assets/fonts/: Noto Sans TC Bold is the one the SVG asks for by name, and Noto Sans JP Bold only fills in glyphs TC does not have (Japanese kanji such as 盗). The front end lists both in a CSS font-family on svg text, the server hands both to resvg's fontFiles while defaultFontFamily stays Noto Sans TC — the font-family written into the SVG never changes, so shared links keep rendering byte-for-byte identically. The image installs no system fonts.
Docker
The Dockerfile lives in deploy/ but expects the repository root as its build context:
pnpm docker:build # docker build -f deploy/Dockerfile -t venn-diagram-generator .
docker run --rm -p 3000:3000 -e VENN_WATERMARK=venn.example.com venn-diagram-generator
deploy/compose.yml builds that image and publishes it behind a reverse proxy (Traefik labels, external network web, TLS terminated upstream). Every site-specific value in it is an environment variable — it will refuse to start until you supply VENN_PUBLIC_HOST. deploy/compose.dev.yml skips the image entirely: it mounts the source into node:24-slim and runs tsx watch server/index.ts, so both front-end HMR and server restarts work without rebuilding.
Running compose by hand: it only auto-loads the .env sitting next to the compose file (deploy/.env), so pass the repository-root one explicitly — docker compose --env-file .env -f deploy/compose.yml up -d --build.
deploy/deploy.sh is the whole deployment story — there is no registry. It rsyncs the working tree to a host over ssh (skipping .env, so the host keeps its own) and runs compose there with --env-file .env:
VENN_DEPLOY_HOST=my-host VENN_DEPLOY_PATH=/srv/apps/venn ./deploy/deploy.sh
The script sources the repository-root .env first, so those two variables can live there instead of being typed every time (values in .env win over ones already exported).
Prerequisites on that host: the ssh user must be able to run Docker without an interactive password — either in the docker group or with passwordless sudo — and ${VENN_DEPLOY_PATH}/.env must already exist. The script checks that the file declares VENN_PUBLIC_HOST, VENN_GTM_ID and VENN_WATERMARK (empty values are fine, missing keys are not) and exits 1 naming the missing ones before touching anything: a silently dropped watermark would be baked into a year-long cached og:image.
Deployment now checks both the container and the public HTTPS origin after rebuilding: the homepage, /llms.txt (status, text MIME and API content), API documentation/OpenAPI, a CJK SVG and editable link, and real square/OG PNGs. A 404, redirect, HTML fallback, or unexpected X-Venn-Revision makes deployment fail. VENN_REVISION is baked into the image as an OCI revision label and response header; deploy.sh uses the current Git commit with -dirty for an uncommitted working tree. This identifies the source revision, not a digest of dirty files. Running Compose manually without a revision uses unknown.
To inspect an existing deployment without changing it, run pnpm smoke -- https://your-host.example locally, or node dist-server/smoke-check.mjs http://localhost:3000 inside the container. Pass an expected revision as the second argument to detect a stale image. If the internal check passes but the public check fails, inspect proxy host/path routing and cached errors; if both fail, inspect the running image/server bundle. A successful local check does not establish production availability.
Environment variables
Copy .env.example to .env in the repository root and fill it in — on the deployment host, that is the file compose reads. Nothing the server does has a baked-in default pointing at someone else's infrastructure: no hostname, no analytics id, no watermark. The one exception is the CLI's share link, which falls back to this project's public instance (see VENN_BASE_URL below) because a link has to point somewhere.
| Variable | Used by | Required | Meaning |
|---|
VENN_PUBLIC_HOST | deploy/compose.yml | yes | Public hostname of your instance. Becomes PUBLIC_ORIGIN and the Traefik Host() rule; compose errors out when it is missing. |
VENN_WATERMARK | server | no | Watermark text at the bottom right of generated images. Unset or empty draws no watermark. |
VENN_GTM_ID | server | no | Google Tag Manager container id. Unset injects no GTM snippet at all — leave it unset unless it is your container. |
PUBLIC_ORIGIN | server, build | no | Absolute origin for og:image / og:url. Unset falls back to the request headers; deploy/compose.yml derives it from VENN_PUBLIC_HOST. |
PORT | server | no | Listen port, default 3000. |
VENN_BASE_URL | venn CLI | no | Origin the CLI puts in share links. --base-url wins over it; unset falls back to https://venn.applepig.net. Point it at your own instance after forking. |
VENN_DEPLOY_HOST | deploy/deploy.sh | yes | ssh target of the deployment host. The script exits 1 and names the missing variable. |
VENN_DEPLOY_PATH | deploy/deploy.sh | yes | Directory on that host to rsync into. |
VENN_DEV_HOST | deploy/compose.dev.yml | yes | Hostname of the source-mounted dev site; compose refuses to start without it. |
VENN_REVISION | Docker build, server | no | Build provenance for the OCI image label and X-Venn-Revision header; generated by deploy.sh. Manual Docker builds can pass --build-arg VENN_REVISION=. |
VENN_DIST | server, build | no | Internal — do not set in production. Build output directory, default . |
Forking
The visual branding is not generic, so swap these before you publish your own instance:
ui/public/og-base.png — the 1200 × 630 social base image with the original project's branding on it. Replace it with your own artwork (same dimensions), then run pnpm build to re-bake dist/og-default-<hash>.png.VENN_WATERMARK — set it to your own hostname, or leave it unset for no watermark.VENN_GTM_ID — set your own container id, or leave it unset so no analytics load at all. Never inherit someone else's.VENN_PUBLIC_HOST / VENN_DEV_HOST — your own hostnames. There are no defaults to forget to change.VENN_BASE_URL and package.json's homepage — the CLI's share links point at this project's instance unless you change both.
Notes
- "Copy image" uses
ClipboardItem and needs a secure context (HTTPS or localhost). Where that is unavailable the UI suggests "Download PNG" instead.
- "Share image" only appears where
navigator.canShare({ files }) accepts a PNG file — on iPadOS and iOS Safari that share sheet is the only way to get the image into Photos ("Save Image"); <a download> stops at Files. Closing the sheet does nothing; any other failure falls back to opening the PNG inline, which you can long-press to add to Photos.
- How much text fits in a region is bounded by its inscribed rectangle. The centre region of a four-circle diagram is especially tight: past roughly four full-width characters the text overflows even at the minimum font size (2.5% of canvas width). Put long sentences in single-circle or two-circle slots.
Licence
Code is MIT — see LICENSE.
The bundled fonts Noto Sans TC Bold and Noto Sans JP Bold are licensed under the SIL Open Font License; its terms are in assets/fonts/OFL.txt (one copy covers both) and travel with the font files.
