Beacon termination

Capture beacon data from the browser, divert beacon request payloads to a log endpoint, and avoid putting load on your own infrastructure.

Fastly Compute

Use this starter

Using the Fastly CLI, create a new project using this starter somewhere on your computer:

$ fastly compute init --from=

Or click the button below to create a GitHub repository, provision a Fastly service, and set up continuous deployment:

Deploy to Fastly

What are beacons?

Beacons are HTTP requests, usually POSTs, sent from a web browser to record some analytics data. Browsers offer native support for beacons via the navigator.sendBeacon method, and via the Reporting API for out-of-band reports on browser-generated warnings like CSP and feature policy violations, deprecations, browser interventions, and network errors. Native apps will also often send beacon data back to base.

For an in-depth guide to beacon termination using VCL, see the Beacon Termination tutorial.


  • Exposes a POST /reports endpoint to receive beacon reports (in batches)
  • Deserializes individual reports from JSON to Rust data structures, with optional type-checking (see Payload examples)
  • Enriches the data with information available at the edge, e.g. by adding geo data
  • Sends reports to a logging endpoint as individual JSON lines N.B.: Depending on which logging endpoint type is chosen, these lines may be batched.
  • Responds with a synthetic 204

Payload examples

This starter kit allows an individual report to be any valid JSON value.

For optional type-checking, it also includes the data structures for some common report payloads. These structures can be imported from modules following the example_... naming convention:

  • CSP Violations
    mod example_csp_violation;
    use crate::example_csp_violation::ReportBody;
  • Network Errors
    mod example_network_error_log;
    use crate::example_network_error_log::ReportBody;
  • Core Web Vitals
    mod example_core_web_vital;
    use crate::example_core_web_vital::ReportBody;
    Tip: Use the web-vitals JavaScript library to measure all the Core Web Vitals.


The following resources need to exist on your active Fastly service version for this starter kit to work:

Next steps

Starters are a good way to bootstrap a project. For more specific use cases, and answers to common problems, try our library of code examples.