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Open‑source, client‑side browser fingerprinting library that generates stable anchor‑based visitor IDs entirely in the browser, with no backend or API key

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Open-source, purely client-side browser fingerprinting that computes a stable anchor-based visitor identifier without any API keys or backend calls.

### What is GuardianJS?

GuardianJS is a lightweight library that:

- **Collects rich browser and device signals** via the Guardian JS Agent.
- **Builds a stable “anchor” signature** from GPU/WebGL, hardware, audio, math, and timing signals.
- **Hashes the anchor into a `visitorId`** that stays reasonably stable across sessions and incognito mode on the same device.

Everything runs **entirely in the browser** – no data is sent to Guardian, and no Guardian API key is required.

> **Note**: GuardianJS Free is designed for experimentation, prototyping, and low-risk use cases. For production-grade fraud prevention and far fewer false positives, you should use **Guardian Pro** instead (see below).

### Demo

Visit [GuardianJS vs Guardian Pro Demo](https://demo.guardianstack.ai) to see your visitor identifier.

Now, try visiting the same page in private / incognito mode and notice how the visitor identifier remains the **same**!

### Installation

```bash
npm install @guardianstack/guardianjs-free
```

or

```bash
yarn add @guardianstack/guardianjs-free
```

### Basic usage

GuardianJS mirrors the ergonomics of popular fingerprinting libraries: you **load** the agent once, then **get** the visitor identifier when needed.

```ts
import GuardianJS from "@guardianstack/guardianjs-free";

// Initialize GuardianJS at application startup
const guardianPromise = GuardianJS.load({ debug: false });

// Later, when you need a visitor identifier
guardianPromise
  .then((agent) => agent.get())
  .then((result) => {
    // Stable, anchor-based visitor identifier
    const visitorId = result.visitorId;

// Structured anchor payload (GPU/WebGL/hardware/audio/math/timing)
    const anchor = result.anchor;

// Full browser signals as collected by the Guardian JS Agent
    const signals = result.signals;

console.log("visitorId", visitorId);
  });
```

#### API surface

- **`load(options?: LoadOptions): Promise<Agent>`**
 - **`debug?: boolean`**: when true, `agent.get()` will print timing and anchor details to the console.
- **`Agent.get(options?: GetOptions): Promise<GetResult>`**
 - **`GetResult.visitorId: string`**: the anchor-based visitor identifier.
 - **`GetResult.anchor: Record<string, unknown>`**: normalized anchor payload.
 - **`GetResult.signals: BrowserSignals`**: raw browser signals from the Guardian JS Agent.
 - **`GetResult.version: string`**: GuardianJS library version.

GuardianJS Free never attempts to contact the Guardian backend – it only reads browser APIs and computes identifiers locally.

### Limitations

#### Accuracy

Since GuardianJS Free processes and generates the fingerprints from within the browser itself, the accuracy is significantly lower than in the commercial version. Different users with identical hardware/software setups may share the same `visitorId`.

#### Security

Because the fingerprints are processed and generated entirely on the client, they are vulnerable to spoofing, replay attacks, and reverse engineering.

### Industry-leading accuracy with Guardian Pro

The main difference between GuardianJS Free and **Guardian Pro** lies in the number of attributes collected, how they are processed, and the accuracy in identifying visitors.

Guardian Pro is a **closed-source, commercial** device intelligence platform designed to prevent fraud and improve user experiences. It is an enhanced version of the open-source strategy and has been fully re-designed to solve the most challenging identification use cases.

Unlike GuardianJS Free, Guardian Pro achieves **industry-leading accuracy** because it:

- Processes browser attributes on the server to verify integrity.
- Analyzes vast amounts of auxiliary data (IP addresses, ASN, network routes, time-of-visit patterns).
- Uses advanced fuzzy matching to reliably deduplicate different visitors that have identical devices.
- Detects bots, automation tools, and spoofing attempts.

Guardian Pro is available for Web and native platforms. You can easily get started by signing up for a free trial.

### GuardianJS Free vs. Guardian Pro

The table below compares and contrasts these two products:

👉 **If you care about minimizing false positives and reliably catching bad actors, Guardian Pro is what you want in production.**

You can get started in minutes by signing up at:  
**[https://dashboard.guardianstack.ai](https://dashboard.guardianstack.ai)**

### License and contributions

- **License**: GuardianJS is released under the MIT license (see `LICENSE`).
- **Contributions**: Issues and pull requests are welcome. If you plan a significant change, consider opening an issue first to discuss the approach.

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