Free SEO Audit: GSC, Screaming Frog & Lighthouse
Semrush costs $139/month. Ahrefs costs $129/month. For solo site owners and freelancers, that’s serious money — nearly $1,700/year, equivalent to hosting costs for a mid-size site.
The good news: three free tools cover 80% of a professional SEO audit. That $139/month you save can go toward links, ads, or just staying profitable.
The tools: Google Search Console, Screaming Frog SEO Spider, and Lighthouse.
Tool Comparison
| Tool | Coverage | Free Limit | Key Use |
|---|---|---|---|
| Google Search Console | Index status, search performance, CWV | Unlimited | Macro health check |
| Screaming Frog | Full-site crawl, 200+ metrics | 500 URLs free | Micro issue scan |
| Lighthouse | Page-level performance/SEO/a11y | Unlimited | Deep page diagnostics |
These three complement each other: GSC shows trends, Screaming Frog finds bugs, Lighthouse diagnoses depth. You need all three.
01. GSC — Macro Health Check (30 min)
GSC is the only tool that tells you how Google sees your site. It’s your SEO health screening center.
1.1 Pages Report
Open the “Pages” report in the left sidebar. Watch two numbers:
- Valid pages: Is the count growing or shrinking? Two consecutive months of decline = a problem.
- Excluded pages: Focus on “Crawled but not indexed” count.
If the exclusion ratio exceeds 20%, you have a serious issue. Google crawled your pages but decided they weren’t worth indexing — usually a content quality problem.
1.2 Performance Report
Set filters: last 3 months, sort by position. Find keywords at positions 4-10 — the “low-hanging fruit” of SEO.
Keywords at positions 4-10 only need minor tweaks (title optimization, content expansion, internal links) to break into the top 3. Keywords at positions 11-20 are a tier harder. Don’t start with them.
Export CSV, add a “Priority” column using these rules:
- Position 4-7 → High priority
- Position 8-10 → Medium priority
- Impressions > 100 and position > 10 → Monitor
1.3 Core Web Vitals Report
Switch to the “Mobile” tab. Check two things:
- Number of URLs in “Poor” status
- Break down by issue type: LCP > 2.5s is the most common
Root cause in most cases: unoptimized images. A single 2MB PNG can drive LCP past 4 seconds.
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1.4 Sitemaps Section
Is the submitted sitemap status “Success”? Compare “Submitted URLs” vs. “Indexed URLs” ratio.
Ratio < 50% = crawl budget or content quality issue. Go back to Screaming Frog to analyze which pages aren’t getting indexed.
What GSC can’t do: find 404s, detect duplicate titles, identify missing H1s, or surface oversized images. That’s what offline tools are for.
02. Screaming Frog — Micro Issue Scan (1 hour)
Screaming Frog SEO Spider free version handles 500 URLs. For most personal sites and SMBs, that’s enough.
2.1 Crawl Setup
Three steps before you start:
- Enter site URL, click “Start”
- Configuration → Spider → Check “Crawl Images”, “Crawl CSS”, “Crawl JavaScript”
- Configuration → User-Agent → Select “Googlebot (Smartphone)”
Using Googlebot’s User-Agent shows you what Google sees — not what users see. Some JS rendering issues only surface from the crawler’s perspective.
Crawl time: ~5-10 minutes for 500 URLs.
2.2 Key Columns to Export
After crawling, export CSV. Focus on these columns:
| Column | What to Check | Severity |
|---|---|---|
| Status Code | All 404, 301, 302, 500 | High |
| Title 1 | Duplicate titles (sort alphabetically to spot patterns) | High |
| H1-1 | Missing or duplicate H1s | Medium |
| Meta Description 1 | Missing, too short (< 70 chars), too long (> 160 chars) | Medium |
| Canonical Link Element 1 | Missing canonical tag | High |
| Image Size | Sort descending, find anything > 500KB | High |
| Internal Links | Pages with 0 internal links (orphan pages) | High |
| Click Depth | Depth > 4 (hard for Google to find) | Medium |
2.3 Image-Specific Audit
Filter “Images” under the Internal tab. Three checks:
- File size > 500KB: These images directly bloat LCP. An 800KB product photo isn’t worth it.
- Dimensions > 2000px wide: Display width is usually 800px — you’re wasting 60% of bandwidth.
- No Alt text: SEO blind spot. Google Image Search uses Alt text to understand image content.
👉 TinyOpt batch-compresses + converts format, shrinking >500KB images to <150KB
2.4 Hreflang Audit
If your site is multilingual, check hreflang tags:
- Do any hreflang links point to 404 pages?
- Are any language versions missing?
- Is x-default correctly configured?
Wrong hreflang = Google might serve English pages to French users.
03. Lighthouse — Page-Level Diagnostics (30 min)
Lighthouse is built into Chrome DevTools. Completely free, unlimited use.
3.1 How to Run
Open Chrome DevTools (F12) → Lighthouse tab → Run Desktop + Mobile separately.
Recommended pages: homepage + 3 core landing pages + 1 blog post. These 5 pages represent your site’s typical performance.
3.2 Performance Deep Dive
Performance score < 50 = serious issues. Check two key areas:
LCP element: What’s the largest visible element? If it’s an <img>, verify three things:
- Is it compressed? (Original > 500KB = fail)
- Is the format WebP/AVIF or JPEG/PNG?
- Does it have
loading="lazy"and explicit dimensions?
Opportunities → “Serve images in next-gen formats”: This is Lighthouse’s #1 image-related suggestion. Switch to WebP/AVIF to resolve it instantly.
👉 TinyOpt converts to WebP/AVIF in one click, eliminating Lighthouse image warnings
3.3 SEO Checks
Lighthouse’s SEO audit covers 15+ basic checks:
Document has a <title> element: Basic but often missed (especially in SPAs)Links have descriptive text: “Click here” and “Learn more” are SEO dead weightrobots.txt is valid: One wrong character can block your entire site- Structured data validation: Lighthouse flags Schema syntax errors
Pass every single one. SEO score < 90 means fix them item by item.
Audit Report Template
After each audit, organize findings into three pages:
Page 1: Executive Summary
- Top 3 most critical issues
- Estimated fix time for each
- Expected SEO impact (ranking / indexing / speed)
Page 2: Priority List
| Priority | Issue | Pages Affected | Fix Difficulty | Est. Time |
|---|---|---|---|---|
| P0 | Fix all 404s | 12 | Low | 30 min |
| P1 | Compress images >500KB | 34 | Low | 20 min |
| P2 | Add missing H1s | 8 | Low | 15 min |
| P3 | Fix duplicate titles | 15 | Medium | 1 hour |
Sort by impact × fix difficulty. High impact + easy fix = do first.
Page 3: Progress Tracker
| Week | Planned Fixes | Completed | Notes |
|---|---|---|---|
| Week 1 | 404s + image compression | ✓ | One-time fixes |
| Week 2 | Titles + H1s | ✓ | Page by page |
| Week 3 | Canonical + Schema | Pending | Needs dev help |
Pattern Summary
Paid SEO tools add convenience, not capability. The three free tools in this guide give you the same diagnostic power.
Paid tools only add value in three areas:
- Scale: Full-site audits beyond 500 URLs
- Trend tracking: Automated period-over-period comparisons
- Competitor analysis: Insight into competitors’ keyword strategies
Recommended path: start with free tools. Only upgrade when your site exceeds 500 pages. Until then, that $139/month is better spent on content creation or link building.
FAQ
Q1: Can Screaming Frog crawl large sites?
Free version caps at 500 URLs. Beyond that, you need a license (￡199/year, ~$260). For most personal sites and SMBs, 500 URLs is sufficient.
Q2: Are Lighthouse scores the same as real-user experience?
Not exactly. Lighthouse is lab data (simulated environment); GSC Core Web Vitals are field data (real users). Discrepancies can occur. Trust GSC data as the source of truth, use Lighthouse as an issue discovery tool.
Q3: Do I need Screaming Frog if I already use GSC?
Yes. GSC won’t tell you which pages have duplicate titles, which images exceed 500KB, or which pages are orphans. GSC is macro, Screaming Frog is micro — you need both.
Q4: What if I find 50 image issues — how do I batch-fix them?
Manual fixes are impractical. Use TinyOpt for batch import — compress, convert format, and resize all at once. 50 images fixed in minutes.
👉 TinyOpt batch processing — one click solves all your image optimization issues
Q5: How often should I run this audit?
Monthly. 2 hours each time catches most problems. Run an extra one after major content pushes or site redesigns.
Summary
2 hours. 3 free tools. 80% coverage of a professional SEO audit.
This is the best 2 hours you’ll spend on SEO each month. Better than chasing trends, better than fretting over algorithm updates, better than any other SEO investment — because it tells you exactly what’s wrong, how to fix it, and what will happen when you do.
Remember the workflow:
- GSC shows you how Google sees your site
- Screaming Frog reveals the problems you don’t know about
- Lighthouse diagnoses each page’s specific symptoms
Open GSC this afternoon. Follow Step 1 from this guide. In 30 minutes, you’ll spot an issue you hadn’t noticed before.
👉 Download TinyOpt — fix every image issue Lighthouse flagged, all at once
TinyOpt Team
The team behind the TinyOpt open-source project, focused on building and optimizing desktop image processing tools. We help designers, front-end developers, and content creators process images in bulk — efficiently and for free.