stan web IDE#

Run Stan sampling in your browser, inside a VS Code-style IDE built on minwebide. Projects live in your browser's IndexedDB. Models compile on a remote stan-wasm-server; sampling itself runs locally in a web worker with tinystan, chains in parallel threads.

Live site: https://concept-collection.github.io/stan-web-ide/

How it works#

A project holds .stan programs, .json data files, and .sample files. A .sample file is a YAML description of one sampling run:

stan: linear.stan      # the Stan program
data: data.json        # the data
output_dir: out/fit    # results are written here (replaced on each run)
num_chains: 4          # optional; defaults 4 / 1000 / 1000 / 2.0 / random
num_warmup: 1000
num_samples: 1000
init_radius: 2.0
seed: 42               # omit for a random seed

Paths are relative to the .sample file (leading / = project root). Opening a .sample file shows a form view — file pickers, sampling parameters, a Run button, and per-chain progress bars. The form edits the underlying YAML (tab menu → Reopen as Text Editor for the raw file); the tab bar's ▶/⏹ runs and stops the same way. Runs use current editor contents, saved or not.

A run compiles the program (server-side, cached by source hash), streams Stan's console output to the Output panel, and writes into output_dir:

• chain_1.csv … one CSV per chain, header = parameter names, one row per draw
• summary.csv — mean, MCSE, sd, 5%/50%/95%, ESS, ESS/s, split-Rhat per parameter (via mcmc-stats)
• sampling_opts.json — the exact configuration used (including the resolved seed)
• console.txt — the sampler's console output

The .stan editor has syntax highlighting plus diagnostics, hover docs, completion, and auto-format from stan-language-server (stanc3 compiled to JS, running in a worker).

The compilation server#

Compiling Stan to WebAssembly needs a server; everything else is local. The status bar shows the configured server (click it to change; persisted in the browser). The default is http://localhost:8083 — run one with:

docker run -p 8083:8080 -it ghcr.io/flatironinstitute/stan-wasm-server:latest

CORS: the server's allowlist must include the page's origin. The stock image allows http://127.0.0.1:3000 and http://127.0.0.1:4173, which match this app's dev and preview ports — open the 127.0.0.1 URL, not localhost. To serve other origins (like the live site above), host a server whose allowlist includes them.

Threaded sampling requires cross-origin isolation (SharedArrayBuffer): dev/preview send COOP/COEP headers; the GitHub Pages deployment uses coi-serviceworker.js, injected at build time only.

Development#

minwebide is consumed as a sibling checkout (file:../minwebide):

git clone https://github.com/magland/minwebide ../minwebide
(cd ../minwebide && npm install)   # fetches the pinned VS Code source
npm install
npm run dev                        # http://127.0.0.1:3000

• npm run build — static bundle in dist/
• npm run typecheck — typechecks app code (vendor diagnostics suppressed)
• npm run smoke — headless end-to-end test against the built bundle; with a compile server on localhost:8083 it also compiles and samples for real
• node scripts/dev-check.mjs — quick checks against a running dev server

CI checks out magland/minwebide next to this repo, installs both, builds, and publishes dist/ to GitHub Pages.