Glossary
Terms used across fastmon, the dashboard, and this documentation.
Compact definitions. For depth, follow the link on each term.
Web Vitals
LCP: Largest Contentful Paint. Time until the largest visible element renders. The load metric. Good ≤ 2,500 ms at p75. See LCP.
INP: Interaction to Next Paint. Worst-case latency between interaction and the next paint. The responsiveness metric. Good ≤ 200 ms at p75. Replaced FID in March 2024. See INP.
CLS: Cumulative Layout Shift. Sum of unexpected layout shifts. Unitless. The visual-stability metric. Good ≤ 0.1 at p75. See CLS.
FCP: First Contentful Paint. Time until the first text or image renders. Diagnostic; explains slow LCP. See FCP.
TTFB: Time to First Byte. Time until the first response byte arrives. Diagnostic; the floor for FCP and LCP. See TTFB.
Experience Score: Composite score from 0.0 to 10.0, weighted across LCP, INP, CLS, FCP, TTFB, page-load time, and error rate. Mapped to letter grades A+ through F. See Experience Score.
Core Web Vitals: Google's three-metric set: LCP, INP, CLS. The metrics that affect search ranking.
Beacon and ingestion
Beacon: A single batched payload the tracker POSTs to /c/{collector_hash}. Also shorthand for the script at /s/{source_hash}.js that produces them. See The RUM Beacon.
Tracker: The running JavaScript agent the beacon script starts in the visitor's browser. It registers the observers, buffers values, strips URLs, and sends the beacons.
Collector: The server endpoint at /c/{collector_hash} that receives beacons, validates them, and writes them to the analytics store.
source_hash: Per-application hash in the script URL. Stable across beacon upgrades.
collector_hash: Per-application hash in the ingest URL. Distinct from source_hash so the script template can change without invalidating data.
Preset: A starting point picked when you create an application: Minimal, Standard (default), Full. It fills the application's tracker settings at once; after that each setting is independent. See Presets.
Page-view ID (pvid): Per-page-view identifier the tracker generates client-side. Not persisted.
pst / cst: Page-started timestamp / client-sent-at timestamp. Both visitor wall-clock, in milliseconds since epoch. The interval cst - pst is the reliable clock-skew-free measure of how long the page-view took before flushing.
Resources and accounts
Organization: Top-level account container. Owns applications, members, notification rules, API tokens. See Organizations.
Application: One tracking snippet. Owns the served bundle, both hashes, and every tracker setting, and serves one or more sites. See Applications.
Plan: Organization tier: beta, starter, pro, partner, enterprise. Gates features and quotas.
Site: One domain under an application, with its own dashboard and traffic. The hashes and collection settings live on the application; a site carries only per-domain overrides. See Sites.
Visitor: A distinct visitor, counted along an identity axis: stitch (edge-derived, present in every mode, the default) or session (consent-gated). Anonymous by construction. See Visitors and sessions.
Session: A 30-minute window of page-views from the same browser, grouped by session_id. One of the two visitor identities, and consent-gated. See Visitors and sessions.
Release: Versioned deploy marker, scoped to an application. Used by analytics compare_to_release_id for before/after comparisons. See Releases.
Tag: Free-form label on a site (max 10) for organizing sites. Cross-site analytics scoping by tag is planned; tags don't filter analytics yet. Conventions: env:production, team:growth, etc.
Member: User attached to an organization with a role (owner / member).
Invite: Pending membership awaiting acceptance.
API token: fm_…-prefixed bearer token for programmatic access. Hashed server-side; lost tokens are unrecoverable.
Storage and infrastructure
Configuration DB: Relational store for users, organizations, sites, settings.
Analytics store: Columnar store for beacon events and aggregated metrics.
Session store: In-memory store for sessions, rate limits, short-lived caches.
Partner client: A sub-organization a partner-plan org operates on behalf of someone else.
API
Envelope: Wrapper around the response body. Single resource = raw; list = data + meta; error = error. See API overview.
Cursor pagination: High-volume endpoints return meta.next_cursor; client sends it back as ?cursor=…. See Pagination.
Offset pagination: Default scheme. ?limit and ?offset, response includes meta.total and meta.has_more.
X-Request-ID: Header on every response. Mirrored into error.request_id on failure. Always include when reporting issues.
UUID v7: Time-sortable UUID format used for all resource IDs.
Other
RUM: Real User Monitoring. Measuring performance from real visitor browsers, as opposed to synthetic tests in a lab.
LoAF: Long Animation Frame. Browser API exposing frames that took longer than 50 ms; usually the root cause of bad INP.
Third-party: A request to a domain different from the site's own. Fastmon groups these by domain and category for impact analysis. See /analytics/third-party.
window.fastmon.grantConsent(): The function your CMP calls after consent to switch on the on-device session-id write (when collect_sessions is on). There is no mid-session revoke: the session id is tab-scoped, so declining just means the write never happens. See Consent and the TDDDG.