Reproducing

The pinned target#

Machine-readable in agent/pin.json, which also carries the sha256 of each derived file npm run verify accepted.

Shelf life. The tenant ships new builds and the path segments rotate. Between 2026-07-31 and 2026-08-07 the bundle went from 192,978 to 194,100 bytes with no change to the loader tag or the ex build marker, and npm run diff reported 0 signals added, 0 removed, 56 changed. Everything under reference/ describes the pinned build only.

Install#

npm install
npm run fetch

npm run fetch downloads the pinned URL, writes artifacts/agent.original.js, and compares the hash against agent/pin.json. A mismatch means the tenant has shipped a new build: snapshot the current map with npm run diff -- --save <label> before regenerating anything, then read the diff.

Rebuild everything#

npm run all

That is fetch, then deobfuscate (libs, vaults, clean, worker, verify), then map (signals, slice, envelope, endpoints, codes, join, schema, collector, spy). It needs network access for fetch and libs and nothing else; harvest is optional because tools/data/browser-names.json ships with the harvested names.

Expected output on the pinned build:

Take your own captures#

npm run capture

Serves http://localhost:8099/?b=<label>. Open it once per browser. The page loads spy/fpspy.js, imports the stored bundle as a module, calls its exported start() and get(), waits 8 seconds for the delayed stages, and posts the capture back to /save. Nothing is reimplemented and nothing is driven through the npm loader: the bytes the rest of the toolchain analyses are the ones that run.

The tenant answers 403 origin_not_available, because the demo key is bound to its own site. That costs nothing: the spy records the request body inside the fetch hook, before the call leaves, so the payload is captured whatever the server thinks of the origin. The only thing lost is the response, which is a verdict.

Third-party storage entries are dropped on save; npm run scrub does the same to a capture taken earlier.

Watch a live site instead#

npm run spy

Writes spy/fpspy.js, a console script to paste into DevTools on any page running the agent. It hooks fetch, XMLHttpRequest, sendBeacon, Blob/URL.createObjectURL, Worker, the collector-facing browser APIs, and the FingerprintJS global if one appears. See spy/README.md.

Check the wire half#

npm run profile profiles/mac-chrome.json
node tools/replay.mjs --payload artifacts/profiles/mac-chrome.payload.json --dry

--dry builds the frame with the agent's own codec and unseals it locally. A round trip that matches proves the codec extraction has not drifted from the bundle. Everything past --dry sends real requests to a real tenant; 09-toolchain covers those tools and 08-not-determined covers what a server verdict from them is worth.

Run the collectors without the agent#

python3 -m http.server 8123
open http://127.0.0.1:8123/collector/index.html

collector/fp-collect.js is the agent's own collectors with the protection layers folded away. On the machine used here it reports the same status code as the Chrome capture for 132 of the 140 collectors; the eight that differ are the WebRTC pair, which needs the tenant's TURN credentials, and six signals whose result depends on page origin and browser state.