---
title: How Retidal works
description: The four-arc model — Reach, React, Reward, Return — and how the two APIs implement it.
---

Retidal runs on two public HTTP surfaces that together implement four arcs of a single value loop: capture, decide, reward, and account for it.

## Prerequisites

- A Retidal project and a project API key — see [Quickstart](/docs/quickstart).
- The vocabulary in [Core concepts](/docs/core-concepts) — project, event, visitor.

## The four arcs

- **Reach** — attribution and acquisition: every visit and click is captured and attributed, so nothing you paid for is invisible. Ingested through `POST /api/v1/t` and short links (`/s/{code}`).
- **React** — the decisioning engine: `POST /api/v1/decide` evaluates rules in real time and returns a decision for that visitor, without a deploy per rule change.
- **Reward** — incentive execution: once a decision fires, coupons and loyalty mechanics are issued and redeemed (`POST /api/v1/coupons/redeem`).
- **Return** — payback and metering: conversion (metering) events are recorded and returned to the channels and dashboards that need to know, closing the loop back to Reach.

## What this unlocks

Understanding these four arcs unlocks reading every other Get started page as "which arc does this belong to": [Sending data](/docs/sending-data/events) and [Attribution](/docs/attribution/short-links) are Reach, [Decisioning](/docs/decisioning/decide) is React, [Coupons](/docs/decisioning/coupons) is Reward, and metering events close Return.

## Verify it worked

Confirm you can point at Reach's ingestion endpoint and get an ingestion-shaped response, not a 404:

```bash
curl -s -o /dev/null -w "%{http_code}\n" -X POST https://api.retidal.com/api/v1/t
# expect: 401 — no X-API-Key header, but a 401 is Reach's endpoint
# responding (the auth check runs before any not-found routing would apply)
```

## If it doesn't work

If none of the four arcs match what you're trying to do, or a request behaves unexpectedly, work through the [health checklist](/docs/troubleshooting/health-checklist).