# pflow.xyz

> Visual Petri net editor with an embeddable, dependency-free ES module
> library for discrete simulation and continuous (ODE) analysis. All modules
> are served from this origin with `Access-Control-Allow-Origin: *` — import
> them directly from any ad-hoc HTML page, no build step, no npm. ODE
> semantics are behaviorally identical to go-pflow (enforced by a parity
> test suite).

Models are JSON-LD (`@context: https://pflow.xyz/schema`): `places` and
`transitions` are objects keyed by id, `arcs` is an array of
`{source, target, weight}`. `initial`, `capacity`, and `weight` are vectors
(one entry per token color); capacity 0 means unbounded; an explicit 0
weight component means "this color is not involved".

## Docs

- [Full guide](https://pflow.xyz/llms-full.txt): model format, copy-paste
  recipes for solving/plotting/embedding, discrete simulation, related services
- [JSON-LD schema](https://pflow.xyz/schema): the @context served as JSON-LD
- [Book](https://book.pflow.xyz): Petri nets as a universal abstraction

## Modules

- [petri-solver.js](https://pflow.xyz/petri-solver.js): mass-action ODE
  solver (Tsit5, adaptive) + SVGPlotter interactive charts
- [petri-sim.js](https://pflow.xyz/petri-sim.js): discrete firing semantics,
  pure functions
- [petri-colors.js](https://pflow.xyz/petri-colors.js): colored-net unfolding
- [petri-view.js](https://pflow.xyz/petri-view.js): the full `<petri-view>`
  editor web component (with tabbed ODE analysis workbench)
- [petri-view.css](https://pflow.xyz/petri-view.css): editor styles, light +
  dark themes
- [petri-learn.js](https://pflow.xyz/petri-learn.js): differentiable fitting
  for Petri-net ODE models — forward + reverse-mode (adjoint) sensitivities,
  MSE/relative loss gradients, Adam / Nelder-Mead / coordinate-descent,
  `fitRates` convenience
- [petri-ssa.js](https://pflow.xyz/petri-ssa.js): portable Gillespie SSA
  (discrete-stochastic simulation) — byte-exact with go-pflow, pflow-rs and
  pflow-jl via a fixed PRNG (SplitMix64 → xoshiro256**) and a ported log;
  `simulate(model, {horizon, samples, realizations, seed})` → ensemble
  mean/stddev/final per place
- [petri-sde.js](https://pflow.xyz/petri-sde.js): chemical Langevin SDE —
  continuous state with the net's own intrinsic firing noise (Euler-Maruyama
  over the same propensities/stoichiometry `petri-ssa.js` compiles);
  `simulateSDE(model, {horizon, samples, realizations, seed})` → same shape
  as `simulate`, plus `diverged`/`reason`/`caveats` when the model gates
  (read arc, inhibitor, reached capacity — no continuous analogue). Not yet
  byte-exact cross-language the way SSA is.

**Which one for which question**: `petri-solver.js` refuses (rather than
silently mismodeling) a net with a read arc, inhibitor, reached capacity or
guard — use `petri-ssa.js` (or `petri-sde.js`, same refusal) for those, or
whenever token counts are small enough that variance is the answer, not
noise around it; `petri-sde.js` sits between the two — noise, but no
individual discrete events. Above arc weight 1 the three compute genuinely
different rate laws, not a continuous vs. discrete version of the same one.
Full rules: `docs/engine-selection.md` (vendored from go-pflow,
`scripts/docs-sync.sh check`).

## Services

- [Sim MCP server](https://sim.pflow.xyz/mcp): JSON-RPC tools to build,
  run and check models (sim_create_model, sim_scenario, sim_invariants,
  sim_reach, sim_verify, …)
- [Server-side SVG rendering](https://pflow.xyz/api/svg): POST a model,
  get an SVG
- [sim.pflow.xyz](https://sim.pflow.xyz/mcp): describe a process, get a
  model you can run and check — seeded scenarios, invariant and
  reachability proofs, calibration, and diagnostics that rank every knob by
  measured effect on the objective
- [pflow-native](https://github.com/pflow-xyz/pflow-native): native desktop
  editor and simulator for the same models, with a CLI and an MCP server

## Optional

- CDN mirrors for strict-CSP hosts that block pflow.xyz — pin a tag, `@main`
  is cached ~12h by jsDelivr:
  - [jsDelivr](https://cdn.jsdelivr.net/gh/pflow-xyz/pflow-xyz@v1.27.0/public/petri-solver.js)
  - npm-backed (`@pflow-xyz/pflow-xyz` on npm since 2026-08-01):
    `https://esm.sh/@pflow-xyz/pflow-xyz@1.27.0/petri-solver.js` or
    `https://unpkg.com/@pflow-xyz/pflow-xyz@1.27.0/petri-solver.js`
  - cdnjs (pending acceptance — needs 800+ npm downloads/month or 200 GitHub
    stars; placeholder, 404s until then):
    `https://cdnjs.cloudflare.com/ajax/libs/pflow-xyz/<version>/petri-solver.js`
- **claude.ai artifacts cannot load these modules today.** Their CSP allows
  scripts only from `cdnjs.cloudflare.com`; pflow.xyz, jsDelivr, esm.sh, and
  unpkg are all refused (`Failed to fetch dynamically imported module`). Do
  not emit an import-with-fallback loader for artifacts — host the page
  elsewhere instead. Also note `file://` pages can't load ES modules at all;
  open local pages via `python3 -m http.server`.