Gsc Lighthouse

GSC + Lighthouse health check

Pulls Google Search Console (sitemap status, per-URL index coverage, 28-day search analytics) and runs Lighthouse via the PageSpeed Insights API on the top 10 pages by clicks. Produces a single report a non-technical person can read.

The point: most "SEO audit" tools throw a hundred warnings at you. This one tells you what's actually broken, calibrates against false positives, and groups fixes by theme so you can ship a single PR instead of a hundred.

Step 1: Ask the user 2 questions

1. What's your GSC property? (the verified site in Search Console)

• sc-domain:example.com, Domain property (covers all subdomains and protocols)
• https://example.com/, URL-prefix property (one specific protocol + host)
• If they don't know, link them to https://search.google.com/search-console and ask them to copy the property URL from the sidebar.

1. Do you have a PAGESPEED_API_KEY configured? (.env or shell env)

• yes → Lighthouse step runs.
• no / skip → Lighthouse step is skipped, GSC report still ships. (See README.md "Setup: PSI API key" for the 3-command setup, ~30 seconds.)

That's it. No other config needed.

Step 2: Run the audit

cd skills/gsc-lighthouse
python audit.py --site "sc-domain:example.com"

Add --no-lighthouse to skip the PSI step. Add --top N to audit a different number of pages (default 10).

The script writes a JSON dump to ./out/audit-.json and prints the structured report to stdout.

Step 3: Report

Read audit.py's stdout straight back to the user. Don't reformat unless they ask; the script's output is already structured for direct read.

If the user wants a TL;DR, summarize in this shape:

## GSC + Lighthouse: {today}

Sitemap:        {N URLs, errors/warnings}
Indexing:       {indexed} / {total}
Search (28d):   {clicks}, {±%} vs prior 28d
Lighthouse:     median perf {score}, median LCP {seconds}

Top 3 fixes (impact-ordered):
1. {theme}, {N pages affected}, est. {savings}
2. ...
3. ...

Bottom line: {one sentence}

Calibration: don't cry wolf

Apply these mental filters before flagging anything as a "problem":

• **Sitemap submitted 14 days since submission. Younger pages are just queued.
• Single-run Lighthouse perf swing of ±10 points → variance, not regression. Re-run after warming the origin.
• TBT spike > 300ms with stable LCP/FCP → cold-start signature on serverless platforms (Cloud Run, Lambda@Edge). Warm with a curl loop, re-run.
• Lab Lighthouse green but field CWV (CrUX) yellow/red → trust field data. Lab is synthetic; CrUX is what real users experience and what Google ranks on.

Real problems worth flagging:

• Sitemap errors > 0 or warnings > 0
• Canonical mismatches (Google chose a different canonical than declared)
• Pages stuck "Crawled - currently not indexed", Google decided not to index, quality signal
• Pages stuck "Discovered - currently not indexed" > 14 days
• Soft 404s on pages that should be real content
• Sudden traffic drops > 30% week-over-week
• Sitemap URLs returning 404 or redirecting
• LCP > 4s on top traffic pages (poor band, ranking penalty)
• Console errors from third-party tags

Output style guide

When you write the report (Step 3), follow these rules:

• Group fixes by theme, not by page. "10 pages need image optimization" beats listing the same fix 10 times.
• Sort by impact × ease. A 3KB CSS purge that saves 200ms across all pages beats a 1MB image swap on one low-traffic page.
• No emoji unless something is genuinely broken. This is a diagnostic report, not a slide.
• Be specific in ms / KB savings when PSI gives them. "Reduce unused JS (-1050ms)" beats "Reduce unused JavaScript".
• If nothing is broken, say so directly. Don't pad.

Setup: PSI API key

Anonymous PageSpeed Insights API hits get rate-limited fast (a single IP shares a small daily quota). With a free API key, the limit is 25,000/day, far more than you'll ever need.

# 1. Enable the API on a GCP project (any project, even a fresh one)
gcloud services enable pagespeedonline.googleapis.com --project=YOUR_GCP_PROJECT

# 2. Create the API key
gcloud beta services api-keys create \
  --display-name="PageSpeed Insights" \
  --project=YOUR_GCP_PROJECT \
  --format='value(response.keyString)'

# 3. (Recommended) Restrict the key to PSI-only via the GCP Console:
#    https://console.cloud.google.com/apis/credentials → click the key → API restrictions
#    → "Restrict key" → select "PageSpeed Insights API" only.

# 4. Add to .env in the repo root or wherever you run the script
echo "PAGESPEED_API_KEY=" >> .env

Setup: GSC auth (Application Default Credentials)

Google Search Console doesn't accept service-account emails on Domain properties (known limitation). Use ADC bound to your verified Google Account:

gcloud auth application-default login --scopes=\
https://www.googleapis.com/auth/webmasters.readonly,\
https://www.googleapis.com/auth/webmasters,\
openid,\
https://www.googleapis.com/auth/userinfo.email

Sign in with the Google Account that owns the GSC property. Credentials are saved to ~/.config/gcloud/application_default_credentials.json and any Python script using google.auth.default() picks them up automatically.

If a 401 surfaces during the run, the script will print a clear "re-auth needed" hint with the exact command above.

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: NachoLafuente
• Source: NachoLafuente/5050-gtm
• License: MIT

Install and usage instructions live in the source repository linked above.