# Introduction

> Fingerly identifies the device behind every session and scores how suspicious it is, so your application can stop fraud without adding friction for real people.

Last updated: 2026-09-17

Fingerly is device intelligence for web and mobile applications. At the moments that matter, such as signing up, logging in or paying, it tells you **who** the visitor is and **how suspicious** the session looks, with every signal behind the answer.

## What you get from every identification

| Answer | Field | Use it to |
| --- | --- | --- |
| A stable visitor ID | `visitor_id` | Recognise a returning device across sessions, logouts and cleared storage. |
| How sure that is | `visitor_confidence` | Decide how much to trust the match, from 0 to 100. |
| A suspect score and level | `suspect_score`, `suspect_level` | Allow, challenge or review, against a threshold you control. |
| The signals behind it | `triggers` | See exactly why: Tor, a VPN, automation, a rooted phone, tampering and more. |
| Network context | `country_code`, `asn`, `anonymity_network` | Understand where the session really comes from. |

## How an integration fits together

1. A **client SDK** in your web page or app identifies the visitor with a public key and returns a `request_id`.
2. Your frontend sends the `request_id` to your **backend** along with the action, such as the login form.
3. Your backend reads the stored result with a **secret key**, checks it belongs to this action, and decides.
4. **Webhooks** push every result to your systems as it happens, if you want them.

The score never leaves your control. Fingerly does not block anyone on its own: it gives you evidence, and your code makes the decision.

## Start here

- [Quick start](https://docs.fingerly.io/docs/quick-start): Identify your first visitor and verify it on your server.
- [How Fingerly works](https://docs.fingerly.io/docs/how-it-works): From collected signals to a scored, stored event.
- [Choose an SDK](https://docs.fingerly.io/docs/sdks): Web, mobile and server SDKs.
- [API reference](https://docs.fingerly.io/reference/overview): Every endpoint, field and error.

## Principles

- **Outcomes, explained.** Every score lists the signals and weights that produced it.
- **Your policy.** Weights and thresholds are yours to tune, per organization or per key.
- **No interruptions.** No SDK ever shows a permission prompt or a dialog to your visitors.
- **Free to build.** Development and staging keys run the same detection as production and cost nothing.