scanner-first · ai-enhanced

Find the JavaScript SEO problems your normal crawler misses.

Crawlfix compares your raw HTML against the fully rendered DOM to find the JavaScript SEO problems your normal crawler misses, then gives your developer or AI coding agent exact repair instructions.

View example report✓No card required · ~30 seconds

Before JS

421words · 11 links

what the crawler gets first

After hydration

1,834words · 58 links

what the user actually sees

built forNext.jsReactVueNuxtSvelteKitAngularRemix

crawlfix.ai/scan/new

ready

Free scan · no card required

Scan any web app

We'll fetch your raw HTML, render it in real Chromium, and diff the two.

Try:

✓SEO + accessibility audit · ~30 secondsscanner v0.4.2

§ 01

The gap

Your site looks perfect in a browser. The first HTML response tells a different story.

Many JavaScript-heavy sites send weak, empty, delayed, or unstable HTML to crawlers. Generic SEO tools rarely inspect the difference. Crawlfix focuses on what the server sends first vs. what the browser shows after JavaScript runs.

EMPTY_SHELL

Empty app shell

Raw HTML is mostly a div with a script tag. Nothing meaningful for crawlers to index before JavaScript runs.

META_HYDRATE

Title / meta changes after hydration

Initial response says "Loading…". The real title only appears once your client-side router resolves.

LINKS_CSR

Client-only internal links

Your nav and product links are bound by JS. Raw HTML lists 11; rendered DOM lists 58.

SCHEMA_CSR

Client-only JSON-LD

Product, FAQ, or Article schema gets injected after hydration. Most crawlers don't wait.

MAIN_DELAYED

Delayed main content

<main> is empty until a fetch resolves. The first HTML response carries a spinner, not your page.

BUNDLE_PRESSURE

JavaScript bundle pressure

Render-blocking scripts and large JS bundles push the page beyond what crawlers comfortably wait for.

INDEX_FLIP

Indexability changes after render

Pages appear indexable in raw HTML but a useEffect adds noindex once a state condition resolves.

CANONICAL_DRIFT

Canonical / noindex instability

Canonical or robots tags change between raw and rendered HTML, sending mixed signals to crawlers.

Who it's for

A rendering diagnostic, not a rank tracker.

Crawlfix isn't keyword research, backlink tracking, or rank tracking. It's a JavaScript rendering diagnostic with an AI-agent repair-instruction layer for teams that ship SPA-style sites.

Frontend developers (any framework)

Catch SSR/SSG slips and hydration drift before they ship.

Indie SaaS founders

See whether your launch page actually indexes.

Technical SEO consultants

Diagnostics your generic crawler can't do.

SEO & web agencies

Hand clients a real fix plan, not a checklist.

Startup growth teams

Stop losing organic traffic to hydration bugs.

Teams using AI coding agents

Feed Claude Code or Cursor real audit evidence.

§ 02

How it works

A scanner that ends in a fix, not a PDF.

Five steps. The scanner finds the problem. The report explains it. The MCP hands evidence to your AI. Your AI ships the change. Crawlfix verifies the result.

01.
Crawl raw HTML
Fetch the initial HTML before JavaScript runs. Capture status, headers, title, meta, robots, canonical, links, and visible text, exactly what a basic crawler would see.
$ GET / HTTP/1.1 → status 200 · 421 words · 11 internal links
02.
Render with Chromium
Load the page in a real headless browser, wait for hydration to settle, then capture the final DOM, metadata, links, schema, console events, and a screenshot.
$ chromium · waitFor: networkidle + 800ms post-hydrate · 2.41 s
03.
Compare & detect
Diff raw against rendered. Detect unstable or client-only SEO signals: title swaps, schema drift, indexability flips, missing links, late content.
$ diff: title=changed · canonical=changed · links +47 · schema +CSR
04.
Generate fix instructions
Produce prioritized issues with evidence, framework-specific fix recipes, AI-agent prompts, and explicit acceptance criteria. Your dev or your AI does the edits.
$ issues=12 · recipe: app-router/title · accept: rawTitle === rendered
05.
Verify on preview
After your team or your AI agent ships a preview, Crawlfix rescans and reports whether each issue is fixed, partially fixed, or still failing.
$ verify://acme-saas-pr-184.vercel.app · 9/12 fixed · 2 partial · 1 failing

§ 03

What it checks

Every signal a crawler reads, then again after JavaScript settles.

Crawlfix runs the same page twice, once as raw HTML, once after Chromium hydrates it, and surfaces every place those two views disagree.

Raw vs rendered

✓Raw HTML content
✓Rendered DOM content
✓H1 / heading hierarchy in raw vs rendered
✓Internal link visibility, raw vs rendered count
✓JSON-LD / schema in raw vs rendered
✓Visible text length and reading order

Hydration stability

✓Title changes after hydration
✓Meta description drift
✓Canonical drift
✓Robots / noindex flips
✓Indexability change after render
✓Client-only navigation patterns

Render & performance

✓Empty app shell detection
✓Delayed main content
✓JavaScript bundle pressure
✓LCP candidate estimate (lab)
✓Console / render errors
✓Failed network requests

AI / LLM hygiene

✓AI / LLM visibility hygiene
✓llms.txt visibility check (rolling out)
✓Framework detection (Next.js, Nuxt, …)
✓Routing pattern detection (App / Pages / SPA)
✓Server-render coverage estimate
✓Stable metadata fingerprint

Surface security

✓Security header audit (CSP, HSTS, X-Frame-Options)
✓Secret / API key pattern scan in HTML & JS
✓Sensitive file exposure probing (.env, .git, backups)
✓Mixed content detection on HTTPS pages
✓Source map public exposure check
✓Server version & X-Powered-By fingerprint leak

Frameworks supported

✓Next.js
✓React SPA
✓Vue
✓Nuxt
✓SvelteKit
✓Angular
✓Remix
✓Astro Islands
✓Custom JS apps

§ 04

Free scan vs full scan

A diagnosis preview, then a full technical report and fix plan.

The free scan tells you whether you have a rendering SEO problem. The full scan gives your developer or your AI coding agent everything they need to fix it.

Free scan

Diagnosis preview

For a quick read on whether your site has a JavaScript rendering SEO problem. No card required.

✓Overall SPA SEO risk score
✓Rendered screenshot
✓Raw vs rendered summary
✓Top 3 detected issues
✓Basic metadata check
✓Basic indexability check
✓Basic heading check
✓Internal link count comparison
✓Short verdict

Run free scan

recommended

Full scan

Technical report + fix plan

Everything your developer or AI coding agent needs to fix the rendering SEO problem and verify the result on a preview deploy.

✓All detected issues
✓Exact raw / rendered evidence per issue
✓Complete metadata diff
✓Full internal link visibility report
✓Full schema visibility report
✓JavaScript rendering risk analysis
✓Developer-ready fix instructions
✓Framework-specific repair recipes
✓Acceptance criteria per issue
✓AI-agent repair prompt
✓Report history & JSON export
✓API access (eligible plans)
✓MCP access (eligible plans)
✓Verification scans

See plans

§ 05

Example report

What a real Crawlfix report looks like.

Pulled from a public scan of a Next.js pricing page. Names anonymized.

Verdict

High JavaScript SEO risk

72/100

acme-saas.app/pricing · scanned 2 hours ago · framework: Next.js (App Router)

Top issues

01Main content appears mostly after JavaScript rendering
02The page title changes after hydration
03Several internal links are missing from the raw HTML
04JSON-LD schema appears only after client rendering
05Canonical tag changed after hydration

Full report includes 12 issues with evidence + fix plan.Open report

Highissue · TITLE_HYDRATION

issue 02 of 12

Title changes after hydration

Evidence

raw HTML <title>

— Loading…

rendered DOM <title>

+ Pricing, Acme SaaS

changed after: 1.14 s · client component path: app/pricing/PriceClient.tsx:42

Why it matters

SEO-critical metadata should be stable in the initial server-rendered HTML. Crawlers, link parsers, social previews, and many AI agents process the first HTML response before JavaScript finishes. They will record "Loading…" instead of your title.

Recommended fix · Next.js App Router

// app/pricing/page.tsx
export const metadata = {
  title: "Pricing, Acme SaaS",
  description: "Simple, predictable pricing.",
};

// Avoid setting document.title from a "use client" component.
// Move route metadata to the server-rendered page or layout file.

Acceptance criteria

✓Raw HTML contains the final title
✓Rendered title matches raw title
✓No client-side title mutation occurs after hydration

recipe · app-router/route-metadata · v3

Copy AI prompt Verify on preview

§ 06

MCP · AI coding agents

Let your AI coding agent read the audit.

Crawlfix MCP connects your account to Claude Code, Cursor, ChatGPT, Windsurf, and custom agents. Your AI edits the code. Crawlfix provides the truth.

claude-code · ~/repos/acme-saas

you Use my Crawlfix MCP. Read the latest scan for this site and fix the highest-priority SEO issue in this repo.

claude Calling crawlfix.get_latest_scan…

Found scan 0xA1F2 for acme-saas.app/pricing. Risk: high (72).

Calling crawlfix.get_issues & get_fix_recipe…

Top issue: TITLE_HYDRATION. Recipe: app-router/route-metadata.

Editing app/pricing/page.tsx, removing document.title from PriceClient.tsx.

you Verify on acme-saas-pr-184.vercel.app.

claude Verified. Raw <title> now matches rendered. 1/1 fixed.

Claude CodeCursorChatGPTWindsurfCustom agents

MCP tools your AI can call

crawlfix.get_latest_scanPull the most recent scan for the active site.
crawlfix.list_scansEnumerate scans with filters and pagination.
crawlfix.get_scan_summaryRisk score, framework, top categories.
crawlfix.get_issuesAll issues for a scan, sorted by priority.
crawlfix.get_issue_evidenceRaw vs rendered evidence for one issue.
crawlfix.get_fix_recipeFramework-specific repair instructions.
crawlfix.get_agent_promptA ready-to-paste prompt for the AI agent.
crawlfix.verify_fix_against_previewRescan a preview URL and report status.

⏻Crawlfix MCP is read-only and instruction-first by default. It does not need production write access to your codebase.

End-to-end workflow

01User scans their site in Crawlfix.
02Crawlfix finds rendering SEO issues.
03User opens Cursor, Claude Code, ChatGPT, Windsurf, or another agent.
04User asks their AI to use Crawlfix MCP.
05AI reads scan evidence and fix recipe.
06AI edits the code locally.
07User deploys a preview.
08AI asks Crawlfix to verify the preview.
09Crawlfix rescans and confirms the fix.

§ 07

API

Same scan engine. Programmatic access.

Run scans from CI, schedule them on a cron, or wire them into your own AI agent. The API surface is intentionally small.

CI/CD SEO checks

Block PRs that regress raw HTML coverage.

Agency reporting

Pull scan data into client dashboards.

Internal dashboards

Track rendering health across teams.

Pre-deployment checks

Scan a preview before merging to main.

Scheduled monitoring

Watch for hydration regressions over time.

Custom AI agent workflows

Plumb scans into your own LLM tooling.

crawlfix.ai/api/v1REST · JSON

POST/api/v1/scansStart a new scan

GET/api/v1/scans/{scan_id}Scan status + summary

GET/api/v1/scans/{scan_id}/issuesAll detected issues

GET/api/v1/scans/{scan_id}/reportFull report (JSON)

POST/api/v1/scans/{scan_id}/verifyVerify on preview URL

Read API docs

§ 08

Verification scans

A scanner that closes the loop.

Crawlfix doesn't just report problems. After your developer or AI coding agent ships a preview, Crawlfix rescans and reports exactly what's fixed.

Original issue

Title changed after hydration

raw

— Loading…

rendered

+ Pricing, Acme SaaS

scan 0xA1F2 · production · 2h ago

Verification result

Passed

FIXED

✓Raw HTML now contains the final title
✓Rendered title matches raw title
✓No client-side title mutation after hydration

verify · acme-saas-pr-184.vercel.app · 38s

Fixed Partially fixed Still failing

§ 09

Pricing

Free for diagnosis. Paid for the fix plan.

The free preview is enough to know whether your site has a JavaScript rendering problem. Paid plans unlock evidence, fix recipes, MCP, and verification.

Free

no card required

1 free scan to see whether you have a problem.

✓1 free scan preview
✓Top 3 issues
✓Rendered screenshot
✓Raw vs rendered summary
✓Risk score + verdict

Run free scan

Starter

$19/mo

for solo devs and indie founders

Full reports for one site you actively work on.

✓10 full scans / month
✓1 domain
✓Full reports & evidence
✓Scan history
✓JSON export

Start with Starter

recommended

Pro

$49/mo

for product teams shipping with AI agents

Verification, MCP, and scheduled scans across a small fleet.

✓50 full scans / month
✓5 domains
✓Read-only API
✓MCP access
✓Weekly scheduled scans
✓Verification scans
✓Priority queue

Choose Pro

Agency

$149/mo

for agencies and consultancies

Multi-domain reporting, monitoring, and team access.

✓250 scans / month
✓50 domains
✓Team access
✓Client reports
✓API + MCP
✓Scheduled monitoring
✓Priority queue

Choose Agency

Credit packs and higher-volume plans available · talk to us

§ 10

Honest limitations

What Crawlfix is not.

A short list, on purpose. We'd rather you trust the things we do say.

×Not a replacement for Search Console

Crawlfix is a rendering diagnostic. Search Console shows how Google sees and reports your site over time.

×No ranking guarantees

We do not, will not, and cannot promise rankings. Anyone who does is selling you something else.

×Lab estimates ≠ field Core Web Vitals

LCP candidate analysis is a lab signal. Real user CWV requires field data from CrUX or RUM.

×Human review still recommended

AI-generated fix recipes should be reviewed before production deploys, especially for routing or metadata changes.

×Read-only by default

Crawlfix MCP and API do not need write access to your codebase. Your developer or your AI does the editing.

×Scanner-first

The scanner finds the problem. The AI helps explain and fix it. We don't dress one up as the other.

§ 11

FAQ

Direct answers, no marketing detours.

No. The free scan preview does not require a card.

scan one URL · ~30 s

See what crawlers may be missing.

Run a free scan and find out whether your JavaScript app is hiding SEO-critical content from crawlers and AI agents.

✓No card required · or view example report