Pixellint

Rust crates.io npm docs.rs license

Pixellint is a spec-first validator for pixels, postbacks, conversion API payloads, and other measurement artifacts. It runs in a terminal, in CI, and in agents, and every finding carries a stable id, a severity, an evidence level, and the document it came from.

Broken pixels cost attribution, QA time, and campaign money. The tooling that exists is fragmented: vendor-specific helpers, enterprise tag auditors, and schema linters that know nothing about ad tech. Pixellint is the open validation layer underneath all of that.

$ pixellint validate url 'https://www.facebook.com/tr?ev=Purchse&[email protected]'
rulepack: core
  ok
rulepack: vendor/meta (vendor: meta)
  error   vendor.meta.param.id.missing   `id` is required on Meta Pixel requests but is not present. It is the numeric Pixel ID from Events Manager.
    fix: Set `id` to the numeric Pixel ID shown in Events Manager.
    docs: https://developers.facebook.com/docs/meta-pixel/get-started
  warning vendor.meta.param.ev.invalid   `ev` is `Purchse`, which is not one of the documented values: PageView, AddPaymentInfo, ...
    fix: Use a standard event name, or confirm the custom event is registered in Events Manager.
    docs: https://developers.facebook.com/docs/meta-pixel/reference
  error   vendor.meta.pii.unhashed_email A parameter carries what looks like a raw email address. Meta requires customer information to be normalized and SHA-256 hashed before it is sent.
    fix: Normalize the value, hash it with SHA-256, and send the hex digest instead of the plain address.
    docs: https://developers.facebook.com/docs/meta-pixel/advanced/advanced-matching

2 error(s), 1 warning(s), 0 info message(s) across 2 rulepack(s).

Server-side events are checked in the body, one event at a time:

$ pixellint validate json '{"data":[{"event_name":"Purchase","event_time":1770000000000,
    "action_source":"website","user_data":{"em":"[email protected]"}}]}'
rulepack: vendor/meta-conversions-api (vendor: meta)
  error   vendor.meta-conversions-api.body.event_time.invalid `event_time` must be at most 10 digits, but `1770000000000` has 13. Meta documents it as a Unix timestamp in seconds...
    fix: Send seconds, not milliseconds: divide a JavaScript `Date.now()` by 1000 and floor it.
  error   vendor.meta-conversions-api.body.purchase_requires_value_and_currency A `Purchase` event is missing `custom_data.value` or `custom_data.currency`.
  error   vendor.meta-conversions-api.body.website_requires_source_url The event is marked `action_source: website` but carries no `event_source_url`.

Install

cargo install pixellint          # CLI
cargo install pixellint-mcp      # MCP server
npm install pixellint            # library, WASM-backed

Or paste a URL into the playground at pixellint.org, which runs the same engine in your browser and sends nothing anywhere.

Use it

QA

Validate an inline artifact, a file with @path, or stdin with -:

pixellint validate url 'https://px.ads.linkedin.com/collect?pid=123456&fmt=gif'
pixellint validate postback @conversion-endpoint.txt --json
curl -s "$TAG_URL" | pixellint validate vast -

If the artifact is still a template with unexpanded macros, say so, and macro rules adjust:

pixellint validate url 'https://example.com/pixel?cb=[CACHEBUSTING]' --state template

CI

pixellint validate exits 0 when the artifact is clean or only produced warnings, 1 when any error-severity finding is present, and 2 on a usage or input problem. That makes it usable as a gate:

- name: Validate tracking artifacts
  run: |
    cargo install pixellint
    pixellint validate url @fixtures/conversion-pixel.txt

Agents

cargo install pixellint-mcp

pixellint-mcp speaks MCP over stdio and exposes three tools:

• list_rulepacks
• list_vendors, optionally filtered by category or attributing a single host
• validate_artifact, taking artifact_kind, artifact, and optional claimed_vendor, expansion_state, rulepacks, except_rulepacks

Responses include the structured findings, the detected vendors, and a severity summary, so an agent can act on the result without parsing prose.

Node and the browser

import { validate, isOk } from "pixellint";

const summary = validate("https://www.facebook.com/tr?ev=Purchase");
isOk(summary); // false, the pixel id is missing

Library

use pixellint_core::{ArtifactKind, Engine, ExpansionState, ValidationOptions, ValidationRequest};

let engine = Engine::default();
let request = ValidationRequest {
    artifact_kind: ArtifactKind::Url,
    artifact: "https://www.facebook.com/tr?id=1234567890123456&ev=PageView".to_string(),
    claimed_vendor: None,
    expansion_state: ExpansionState::Unknown,
};

let summary = engine.validate(&request, &ValidationOptions::default())?;
assert!(summary.is_ok());

Rulepacks

core runs on every URL-like artifact. Vendor packs run only when the artifact targets their endpoints, so you get vendor checks without asking for them, and nothing fires on an endpoint it does not understand. A conversion API body has no endpoint to go by, so those packs claim it by the shape of the payload.

Rulepack	Covers	Evidence
core	URL validity, transport, credentials, fragments, ad-tech macro handling, IAB consent signals	normative
vendor/meta	facebook.com/tr pixel requests	official vendor
vendor/meta-conversions-api	Graph API events edge, URL and JSON event payload	official vendor
vendor/google-analytics	GA4 Measurement Protocol, URL and JSON event payload	official vendor
vendor/google-analytics-collect	The /g/collect transport the Google tag uses in the browser	ecosystem reference
vendor/google-tag-manager	gtm.js, gtag/js, and ns.html loader requests	official vendor
vendor/google-ads-conversion	Google Ads conversion and view-through pixels	official vendor
vendor/floodlight	Campaign Manager Floodlight activity tags	official vendor
vendor/adobe-analytics	Adobe Analytics data collection beacons	official vendor
vendor/pinterest	Pinterest tag requests and the noscript fallback	official vendor
vendor/snapchat	Snap Conversions API v3, URL and JSON event payload	official vendor
vendor/tiktok	TikTok Pixel loader and collection requests	ecosystem reference
vendor/linkedin	LinkedIn conversion image pixels	ecosystem reference
vendor/linkedin-conversions-api	LinkedIn conversion events, single and batched	official vendor
vendor/microsoft-uet	Microsoft Advertising Universal Event Tracking	ecosystem reference
vendor/reddit	Reddit Pixel conversion requests	ecosystem reference
vendor/amplitude	Amplitude HTTP V2 event uploads	official vendor
vendor/mixpanel	Mixpanel track ingestion	official vendor
vendor/posthog	PostHog capture, single and batched	official vendor
vendor/klaviyo	Klaviyo event creation	official vendor
vendor/braze	Braze user track: events, purchases, attributes	official vendor
vendor/segment	Segment HTTP Tracking API, single and batched	official vendor

Vendor directory

Rulepacks cover fifteen endpoint families in depth. The vendor directory covers the rest by attribution: 89 vendors and 217 hosts, so an unrecognized pixel still gets a name.

$ pixellint validate url 'https://trc.taboola.com/actions?a=1'
rulepack: directory (vendor: taboola)
  info  directory.no_rulepack_coverage  This endpoint belongs to Taboola (native). No Pixellint rulepack covers it, so only the core checks ran.

Directory entries make one claim, that a host belongs to a vendor. They carry no parameter contracts, the finding is always info, and attribution never changes an exit code. See docs/VENDOR_DIRECTORY.md.

pixellint list-vendors
pixellint list-vendors --json

Select packs per run:

pixellint validate url "$ARTIFACT" --rulepack core
pixellint validate url "$ARTIFACT" --except vendor/meta
pixellint list-rulepacks --json

Full rule inventory with citations: docs/STANDARDS.md.

Evidence levels

Findings say where their authority comes from, and you can hold packs to different standards accordingly:

• normative: a formal standard such as the WHATWG URL Standard or an RFC
• official_vendor: a parameter contract the vendor publishes, with the URL
• official_template: vendor-published templates or SDK behavior
• ecosystem_reference: consistent real-world behavior the vendor generates in its own UI but does not document
• heuristic: Pixellint's judgment, labeled as such

The manifest loader refuses to compile a pack that claims official_vendor without citing documentation.

Custom rulepacks

Rulepacks are data, not code. First-party vendor packs are written in the same JSON format you can write for an internal endpoint:

{
  "id": "custom/acme",
  "display_name": "Acme internal pixel",
  "description": "Contract for the internal conversion endpoint.",
  "vendor": "acme",
  "source_level": "heuristic",
  "match": { "hosts": ["px.acme.example"], "path_prefixes": ["/collect"] },
  "params": [
    { "name": "aid", "requirement": "required", "format": { "kind": "integer" } },
    { "name": "ev", "requirement": "required", "format": { "kind": "enum", "values": ["view", "purchase"] } }
  ]
}

pixellint validate url 'https://px.acme.example/collect?ev=purchase' --rulepack-file acme.json

The format is documented in docs/RULEPACK_SCHEMA.md.

What Pixellint does not do

• It does not extract artifacts from documents. Callers such as Vastlint parse VAST, HTML, or GTM containers and hand Pixellint the URLs they found. The planned document-level result model is in docs/MULTI_ARTIFACT_SCHEMA.md.
• It does not fire requests or check whether an endpoint responds.
• It does not auto-fix. Findings carry fix hints; applying them is on you.

Evidence

Every rule is backed by tests: unit tests in crates/pixellint-core/src/, a golden corpus in fixtures/ with one directory per rulepack, and integration tests that drive the real CLI binary and the real MCP stdio transport.

cargo test --workspace

Docs

• Standards and rule inventory
• Vendor directory
• npm package
• Rulepack manifest schema
• Architecture
• Roadmap
• Multi-artifact output model

License

Apache-2.0. Pixellint is not affiliated with or endorsed by any vendor named in its rulepacks; see NOTICE.