Watchdog

Watchdog is a lightweight, privacy-first analytics system with fully declarative configuration that aggregates web traffic data and exports it as Prometheus metrics. Unlike traditional analytics platforms, Watchdog stores no raw events, uses no persistent user identifiers, and enforces bounded cardinality by design.

Features

Watchdog is privacy-first in design. There are no cookies, no localStorage or browser fingerprinting. Daily salt rotation prevents cross-day visitor correlation, and there is no raw event storage. We only aggregate metrics. Other noteworthy features:

• Multi-site analytics with optional domain tracking
• Bounded cardinality prevents metric explosion
• Rate limiting and DoS protection
• Graceful shutdown with state persistence
• IPv6 support with proper proxy header handling

See the privacy section for more details on what "guarantees" Watchdog has to offer.

Quick Start

NixOS

The recommended way of using Watchdog is consuming the NixOS module. It handles everything from dependencies to environment setup and Systemd configuration. Simply import the NixOS module provided by this flake, and enable services.watchdog:

{inputs, ...}: {
  imports = [inputs.watchdog.nixosModules.default];

  services.watchdog = {
    enable = true;
    settings = {
      site.domains = ["example.com"];
      server.listen_addr = "127.0.0.1:8080";
    };
  };
}

The settings option is freeform, meaning it'll be serialized to the YAML configuration automatically.

Systemd

On non-NixOS distributions, you may build Watchdog with go build and copy it somewhere that's in your PATH. Usually this is /usr/local/bin for system installations:

# Build
$ go build -o /usr/local/bin/watchdog .

# Install service
$ sudo install -Dm700 contrib/systemd/watchdog.service /etc/systemd/system/
$ sudo systemctl daemon-reload
$ sudo systemctl enable --now watchdog

Binary

You may also run the binary from any path by simply building and running it, but it is generally not very advisable. You may consider something like screen to background the Watchdog process. Though, Systemd is the only supported installation mechanism.

# Build
$ go build -o watchdog .

# Run
$ ./watchdog -config config.yaml

Configuration

Watchdog currently supports configuration via YAML file, environment variables or command-line flags. You may find a more complete reference in the configuration reference document.

Quick Start

Create config.yaml:

site:
  # Single-site analytics
  domains:
    - "example.com"

  # Or multi-site analytics
  # domains:
  #   - "example.com"
  #   - "blog.example.com"
  #   - "shop.example.com"

  salt_rotation: "daily"

  collect:
    pageviews: true
    device: true
    referrer: "domain"
    domain: false # Set to true for multi-site analytics

limits:
  max_paths: 10000
  max_sources: 500
  max_custom_events: 100
  max_events_per_minute: 10000

server:
  listen_addr: "127.0.0.1:8080"

Usage

JavaScript Beacon

Similar to Plausible, Watchdog uses a Javascript beacon to track events. In the most basic case, you must add it to your site in a <script> tag to begin collecting metrics:

<script src="https://analytics.example.com/web/beacon.js" defer></script>

The script beacon also supports a variety of configuration options via data attributions, which you might adjust to your own needs. Some of them are described below:

<!-- Custom API endpoint -->
<script src="/web/beacon.js" data-api="/custom/endpoint" defer></script>

<!-- Track specific domain (multi-site) -->
<script src="/web/beacon.js" data-domain="example.com" defer></script>

<!-- Hash-based routing (for SPAs) -->
<script src="/web/beacon.js" data-hash-mode defer></script>

<!-- Track outbound links -->
<script src="/web/beacon.js" data-outbound-links defer></script>

<!-- Track file downloads (.pdf, .zip, .doc, etc.) -->
<script src="/web/beacon.js" data-file-downloads defer></script>

<!-- Exclude paths (comma-separated) -->
<script src="/web/beacon.js" data-exclude="/admin,/dashboard" defer></script>

<!-- Manual pageview tracking -->
<script src="/web/beacon.js" data-manual defer></script>

<!-- Combine multiple options -->
<script
  src="/web/beacon.js"
  data-hash-mode
  data-outbound-links
  data-file-downloads
  defer
></script>

You can also track custom events as follows:

// Simple event
window.watchdog.track("signup");

// Event with custom referrer
window.watchdog.track("purchase", { referrer: "email-campaign" });

// Manual pageview (when data-manual is set)
window.watchdog.trackPageview();

// Force pageview (bypass duplicate detection)
window.watchdog.trackPageview({ force: true });

Metrics

Unlike most common solutions, Watchdog does not do any data visualisation. It collects and aggregates metrics in a Prometheus-compatible manner at the /metrics endpoint. To scrape and store the time-series data, you will need Prometheus. Grafana is a common solution to visualizing said data.

See the observability documentation for full setup guide. It is, however, recommended to be somewhat knowledgable in those areas before attempting to deploy. There exists a Grafana dashboard with support for multi-host and multi-site deployments provided in the contrib directory.

While not final, some of the metrics collected are as follows:

Traffic metrics:

• web_pageviews_total{path,device,referrer,domain} - Total pageviews
  • domain label only present if site.collect.domain: true
• web_custom_events_total{event} - Custom event counts
• web_daily_unique_visitors - Estimated unique visitors (HyperLogLog)

Health metrics:

• web_path_overflow_total - Paths rejected due to cardinality limit
• web_referrer_overflow_total - Referrers rejected due to limit
• web_event_overflow_total - Custom events rejected due to limit

Privacy

Privacy is a fundamental design constraint for Watchdog, and not a feature. All personally identifiable information is discarded at ingestion. We only keep aggregate counts. Some features worth noting.

No Persistent Identifiers:

• No cookies, localStorage, or fingerprinting
• IP + User-Agent hashed with daily rotating salt
• Hash discarded after HLL insertion

Data Minimization:

• Only collects: domain, path, referrer, screen width
• No raw event storage
• All data aggregated at ingestion

Bounded Cardinality:

• Configurable limits on paths, referrers, events
• Prevents unbounded metric growth
• Overflow tracked separately

GDPR/CCPA Compliance:

• No personal data stored
• Daily salt rotation prevents cross-day correlation
• Aggregate-only analytics

Contributing

Watchdog was built in a very short duration to address a very specific need: replace Plausible and replace it as soon as possible. While I've given the appropriate amount of care to the codebase, there may be unintended bugs or missing features that you'd like to support. In this case, you are very welcome to create issues or PRs.

Building

The recommended way of developing Watchdog is using the Nix flake, for a reproducible toolchain. The default shell already provides everything you need, so you can simply use nix develop or use direnv allow if you use Direnv.

Once you have the dependencies, the workflow is relatively simple. Build and test with Go, and then with Nix to ensure packaging is correct.

# Build binary
$ go build -o watchdog .

# Run tests
$ go test ./...

# Run integration tests
$ go test -tags=integration ./test/...

# Build with Nix
$ nix build

Testing

There's a non-negligible test suite for Watchdog that I'm quite proud of. It tests anything from configuration validation to path normalization and other security features that we'd rather not regress. If working on Watchdog, it is advisable that you add test cases and run the tests before submitting your changes.

# Unit tests
$ go test ./...

# Integration tests (requires build tag)
$ go test -tags=integration ./test/...

# Benchmarks
$ go test -bench=. ./test/...

# Coverage
$ go test -cover ./...