Technology Signals

Introduction

Ful.io holds a record of the technologies each website runs. Technology Signals is what happens when that record changes: the change itself is stored as a dated event, pushed to the people watching that site, and made readable over HTTP.

Watching is done from the Technology Signals page or your watchlist. For single-site lookups and bulk reports, see the developer API.

What is a signal

One signal names one website, one technology and one date, with an event of added or removed. That is the whole unit, which is what makes signals countable, comparable and safe to put on a timeline.

{
  "domain": "example.com",
  "event": "added",
  "date": "2026-10-27",
  "technology": {
    "name": "Klaviyo",
    "slug": "Klaviyo",
    "tech_icon": "Klaviyo.svg",
    "category": "Email Marketing",
    "category_slug": "Email",
    "high_value": true
  }
}

high_value marks commercial tooling that people prospect on, such as payments, ecommerce and marketing platforms, as opposed to plumbing like frameworks and web standards.

The nightly sweep

Recording rules

The digest email

One email per night covering every site you watch, rather than one message per change. Sites are grouped, each with the technologies it picked up and the ones it dropped, and each links to its full timeline. The subject line carries the counts.

Subject: Your watchlist: 3 added and 1 dropped across 2 domains - Technology Signals

Hi there, here's what changed on your watchlist:

getmodern.co (https://ful.io/technology-signals/getmodern.co)
  + Klaviyo (Email Marketing)
  + Segment (Customer Data Platform)

finledger.io (https://ful.io/technology-signals/finledger.io)
  + Stripe (Payment Processors)
  - Braintree (Payment Processors)

Where signals appear

Endpoints

All endpoints are served from https://api.ful.io and return JSON. The feed and the type-ahead are open. The per-domain read is open but returns a shortened stack unless you are signed in, and the three watchlist endpoints act on your own account and require a session.

The newest signals across the whole index, capped at two rows per domain so one freshly rescanned site cannot flood the window. The window is the last 7 days, widened to 30 when that is thin.

Query parameters

Example

curl "https://api.ful.io/signals/feed?limit=10"

Responses carry window_days and an events array of signal objects.

Signal history and summary tiles for a single site. When a domain has no recorded events yet, the response carries a baseline array with the stack currently on file instead.

That baseline is the whole live stack, so signed-out callers receive the highest-value rows only, capped at eight, alongside baseline_total and baseline_truncated. Sign in and the full list comes back, with your watch state attached.

Query parameters

Example

curl "https://api.ful.io/signals/domain?url=example.com&limit=20"

Response fields

Adds a domain to your watchlist. Watching an already-watched domain is treated as a no-op rather than an error, and unwatching keeps the row so history survives.

curl -X POST "https://api.ful.io/signals/watch" \
  -H "Content-Type: application/json" \
  -d '{"domain": "example.com"}'

Related

Errors