Draw the sequence.
Watch it run.

Diagrams are diffable, reviewable, and versioned right next to the code they describe — no drag-and-drop tool to fight, no binary file to merge-conflict.

A flowchart shows what's connected. ArchStep shows what happens: in what order, what runs in parallel, and what data changed, when.

A parallel { } block fires every edge inside it together on screen — fan-out and fan-in render exactly like they run in production.

Already have a sequenceDiagram in Mermaid? Paste it in and get a live ArchStep canvas — no rewrite.

architecture {
  service User at (0, 0)
  service API at (200, 0)
}

Name the services, databases, and queues, and give each a fixed (x, y) — layout is explicit, never auto-guessed.

scenario Checkout {
  User -> API: "place order"
  ...
}

The actual sequence of calls, in order — plus parallel { } blocks and state updates wherever the data tracker should light up.

> Checkout
  User → API

The compiler validates every reference and the canvas animates the sequence tick by tick — step through it, scrub it, or let it run.

git add checkout.step

It's a text file. Review it in a PR, keep it beside the service it documents, and it never quietly drifts out of date.

Play, pause, step one tick at a time, or jump straight to any point in the sequence.

Track one or more named variables through a scenario; every value that changes on a tick highlights the instant it happens.

Model real fan-out/fan-in, not a maze of crossing arrows that all claim to happen "at some point."

Convert a Mermaid sequenceDiagram straight to the canvas, with a tab to peek the generated Step source.