Rein

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Getting started ​

This page builds the rein command and runs a first flow. It needs a Rust toolchain with cargo.

Install the CLI ​

From the repository root, install the binary:

sh
cargo install --path crates/rein
rein --version

If you do not want to install it, run it through cargo from the repository root with cargo run -p rein -- <command>.

Install the editor extension ​

The VS Code extension adds highlighting, diagnostics, and navigation. It uses the same rein binary. See Editor for the steps.

Make a first project ​

A flow is a folder with a main.rein entry point. Flows live in a visible rein/ folder, one subfolder per flow. The project needs no rein.toml. Create a folder named hello with one flow named ticket:

sh
mkdir -p hello/rein/ticket

main.rein is the agent's entry point. This one asks one question and returns one of two instructions. Save it as hello/rein/ticket/main.rein:

rein
/**
 * Decide the next step for a new support ticket.
 */
export default function main(
  /** Is the ticket urgent? */
  urgent: boolean,
) {
  if (urgent) {
    return `Escalate the ticket to on-call now.`;
  }
  return `Answer the ticket from the queue.`;
}

To install a program outside this project, see Install a program.

Check the flow ​

Check the flow for errors. A clean flow prints 0 errors, 0 warnings:

sh
rein check hello/rein/ticket

List the flows ​

From the project folder, list the flows the CLI can see:

sh
rein list

The output shows ticket, its scope, its path, and its description.

Step the flow ​

Step the flow by name. Rein asks for the input it needs and exits with code 2:

sh
rein step --flow ticket --json
json
{"kind":"question","version":1,"key":"main.urgent","function":"main","name":"urgent","type":"boolean","options":null,"description":"Is the ticket urgent?","answers":{},"trace":["main"]}

Give the answer under its key, then step again. The flow ends with kind set to done:

sh
rein step --flow ticket --answer main.urgent=yes --json
json
{"kind":"done","version":1,"instruction":"Escalate the ticket to on-call now.","answers":{"main.urgent":"yes"},"trace":["main"]}

For the full protocol, see spec section 11.

Debug a program ​

Open the flow in the debugger. It serves a page on 127.0.0.1 and opens it in the browser:

sh
rein debug ticket

Set inputs and answers on the left, or answer the current question at the top. On each change the page walks the flow again. It marks the path taken, and shows the next question, the request, or the final instruction. Back removes the last answer. Reset removes all answers. To save a static view, run rein graph ticket --answer main.urgent=yes -o ticket.html.

See the agents that use rein right now, with the step each run waits on:

sh
rein watch

It serves a page on 127.0.0.1 and refreshes it every 2 seconds. It reads the run logs that agents write, and changes nothing. The graph marks the taken steps and the "now" step. Each run shows a status chip. Use the Path and Whole program buttons to switch the graph view.

Next steps ​