Guides
Signals
Every signal the SDK collects, what it measures, and the weight it carries in similarity matching. A signal's weight is how much it distinguishes one device from another, which is its entropy, not merely how stable it is.
Weights come in four tiers. Distinguishing signals are device-specific and decide identity; bucketing signals are near-ubiquitous and only group candidates. The persistence engine page explains how these weights feed the 0.82 / 0.62 similarity thresholds and the entropy gate.
Signal catalog
| Signal | What it is | Weight | Rationale |
|---|---|---|---|
canvas | Hash of a 2D canvas render: text, shapes, blends. | Distinguishing · 4 | High entropy from the exact GPU, driver, and OS text stack. A browser update can rewrite it, so it is never the only signal, but it is a primary distinguisher. |
webgl | Hash of a WebGL scene render. | Distinguishing · 4 | High entropy from the GPU pipeline. Same drift risk as canvas, same importance. |
webglVendor | Full unmasked GPU vendor and renderer string. | Distinguishing · 4 | Distinctive and fairly stable. On Apple Silicon this is the ANGLE-over-Metal string that the chip name is parsed from. |
webgpu | WebGPU adapter info, 30+ hardware limits, and feature flags. | Distinguishing · 4 | The richest hardware signal, 25 to 35 bits of entropy versus 15 to 20 for WebGL. Exposes GPU details WebGL now masks. Available on Chromium and Safari 18+; null on browsers without WebGPU. |
gpuChip | Normalized chip parsed from the renderer: apple-m5, apple-m4-pro, intel, amd, nvidia. | Hard rule · 0 | A physical, immutable property. Used as a negative-only discriminator: a matching chip adds no weight (a whole office may share an M1 Pro), but two SPECIFIC chips that differ hard-split the devices even when every render hash is identical. Generic values (apple-silicon on Safari) never force a split. |
fonts | Set of installed fonts detected by render measurement. | Distinguishing · 4 | User-installed fonts add real entropy on top of the stock OS set, and the set changes slowly. Jaccard overlap tolerates a few additions. |
audio | Hash of an OfflineAudioContext oscillator render. | Distinctive · 3 | Reflects the audio DSP stack. Distinctive, but shifts occasionally, so it sits a tier below the render hashes. |
screen | Resolution including scaling, plus color depth. | Distinctive · 3 | Varies across models and external displays. Docking to a monitor or changing scaling moves it. |
fontPreferences | Measured pixel widths of a probe string across generic and system font stacks. | Distinctive · 3 | Captures subpixel hinting and the OS text stack, higher entropy than font presence. Distinguishing when the rendering pipeline differs. |
speechVoices | Hash of the installed text-to-speech voice set (name, language, local vs cloud). | Distinctive · 3 | Pins the operating system and its version precisely: Windows 11 ships neural voices Windows 10 lacks, macOS has "Samantha" and "Alex", Linux has the eSpeak set. A whole OS-version population shares it. |
hardwareConcurrency | Logical CPU core count reported by the browser. | Population · 2 | Stable, but a whole product line shares one value, so it narrows the field rather than identifying a machine. |
languages | Ordered browser language list, e.g. ["de-DE", "en"]. | Population · 2 | Narrows locale, but millions share "en-US". |
timezone | IANA timezone from the Intl API, e.g. Europe/Berlin. | Population · 2 | Stable and follows the person, but everyone in a city shares it. |
architecture | CPU architecture from Client Hints: arm or x86. | Population · 2 | Cleanly separates Apple Silicon (arm) from Intel Macs (x86) on Chromium, where navigator.platform still reports MacIntel for both. Every Apple Silicon device shares "arm", so it narrows rather than identifies. |
colorGamut, mediaFeatures, mediaDevices, mediaCodecs, webgpuArchitecture | Display gamut, stable CSS media + pointer/hover features, audio/video device counts, the codec support matrix (H.264/HEVC/AV1/VP9/Opus/FLAC), and the WebGPU GPU family. | Population · 2 | Display, input, and codec capabilities add entropy across a population. They shift with an external monitor, an accessibility change, a plugged-in peripheral, or hardware decode support, so they carry moderate weight. |
tlsFingerprint | Server-side JA4/JA3 + HTTP/2 fingerprint of the TLS ClientHello, read from an edge proxy. | Population · 2 | Network-level and impossible to spoof from JavaScript, so a strong bot and browser-family signal. Browser-family level (many share one), and only present when a fingerprinting proxy sits in front. See self-hosting for how to enable it. |
platform, vendor, deviceMemory, colorDepth, touch, platformVersion, mathFingerprint, screenFrame, audioBaseLatency, userAgent | OS platform, browser vendor, RAM bucket, color depth, touch class, OS version, transcendental-math hash, screen insets, audio latency, UA string. | Bucketing · 1 | Near-ubiquitous or fast-changing. Every Mac shares the platform and math stack; screen insets and audio latency add a little entropy. Useful for grouping candidates cheaply, weak for identity. |
ip / asn | Request IP and its autonomous system, resolved server-side. | Network hint | Corroboration only. Mobile devices rotate IPs daily and whole households share one address, so it can nudge a score but never decide a match. |
How to read the tiers
Two devices only merge when their distinguishing signals agree, not when their common signals line up. A browser update that rewrites the canvas and WebGL hashes leaves the GPU renderer, fonts, screen, and audio in agreement, so the same device still re-links. Two different laptops with the same OS, CPU, and browser build differ on the render hashes and GPU renderer, so they stay separate.
Stable is not the same as identifying
Timezone, platform, and core count are stable, but a large population shares each one, so they cannot identify a specific machine. Veriprint weights them low on purpose and reports every match with a confidence score rather than claiming a certain identification.