SEO Lens: Browser Extension for SEO Auditing
TypeScriptChrome ExtensionReactEffect-TSWXTTurboreposhadcn/ui
Chrome extension that audits SEO metadata on any webpage with instant scoring, structured data validation, and AI-friendly copyable reports.
Most SEO tools are cloud-based, slow, and require accounts. SEO Lens runs entirely in your browser — open any page, click the extension, and get an instant audit with a score out of 100. Every finding is copyable as structured text, ready to paste into AI coding agents like Claude Code or Cursor.
The extension uses a crawler-accurate approach: a background service worker fetches the raw HTML (matching what search engines see), not the rendered DOM. Audits re-run automatically on tab switches, SPA navigation, and page focus.
Key Features
Instant Audits
30+ rules across 7 categories — meta tags, headings, social previews, structured data, images, indexing, and site-wide signals. Per-page audits complete in under 150ms.
AI-Friendly Reports
Every finding is copyable as structured plain text. Export full audits as Markdown or JSON — optimized for pasting into AI coding agents for immediate fixes.
Crawler-Accurate
Background service worker fetches the URL and parses raw HTML with DOMParser, matching what a search engine crawler actually sees — not the JavaScript-rendered DOM.
JSON-LD Recommendations
Detects page type (article, product, homepage) and suggests missing structured data with copy-ready JSON-LD templates for Rich Results.
Audit Categories
- Meta Tags — Title length, meta description, charset, viewport, language
- Heading Structure — H1 presence, heading hierarchy, nesting validation
- Social Previews — Open Graph and Twitter Card completeness with visual previews
- Structured Data — JSON-LD validation, Rich Results eligibility, schema recommendations
- Images — Alt text coverage, image optimization signals
- Indexing — Robots meta, canonical URLs, soft-404 detection
- Site-Wide — robots.txt, sitemaps, security.txt, HTTPS checks
Side Panel UI
The extension opens as a Chrome side panel with two tabs:
- Audit — Score out of 100, categorized findings with severity levels, Markdown/JSON export
- Metadata — Full meta tag listing, social preview cards, heading tree visualization, JSON-LD viewer, indexing dashboard
Live audit pipeline re-runs on tab switch, page focus, SPA soft-navigation, or manual refresh — no need to close and reopen.
Architecture
Monorepo Structure
apps/extension— Chrome extension built with WXT + React 19apps/web— Landing page (Next.js)packages/seo-rules— Audit engine built with Effect-TS, fully runtime-agnosticpackages/ui— Shared shadcn/ui components
Why Effect-TS for the Audit Engine
The seo-rules package is the core — a runtime-agnostic audit engine that can run in the browser extension, a CLI, an MCP server, or a desktop app. Effect-TS provides composable rule definitions, typed error handling, and dependency injection that makes the engine portable across any JavaScript runtime.
Roadmap
- Full-site audit — Sampled crawl with URL-pattern grouping
- Additional interfaces — CLI, MCP server, desktop app — all sharing the same
seo-rulescore - Cross-browser — Firefox phase 2; Edge and Safari later
Technology Stack
- TypeScript + Bun — Type-safe development with fast runtime
- WXT + React 19 — Modern Chrome extension framework with React UI
- Effect-TS — Composable, runtime-agnostic audit engine
- Tailwind CSS v4 — Utility-first styling
- shadcn/ui — Accessible UI components
- Turborepo — Monorepo build orchestration
- Vitest — Unit testing for audit rules
- Biome — Linting and formatting via Ultracite preset
Open Source
SEO Lens is free and open source. No account required, no data collection — everything runs locally in your browser. Manifest V3 compliant.