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Free Backlink Data Sources
Reference for the seo-backlinks skill. Loaded on demand when analyzing backlinks
with free sources.
Source Comparison
| Source |
Auth |
Any Domain? |
Data Quality |
Coverage vs Commercial |
Rate Limit |
| Moz API |
API key (free signup) |
Yes |
★★★★☆ |
~70% for DA/PA |
1 req/10s, 2,500 rows/mo |
| Bing Webmaster |
API key (free) |
Verified sites only |
★★★☆☆ |
~15% (Bing index) |
Generous |
| Common Crawl |
None (public) |
Yes |
★★★☆☆ |
~25-40% domains |
N/A |
| Verification Crawler |
None |
Yes |
★★★★★ (binary) |
N/A (checks known links) |
1 req/s per domain |
| DataForSEO (paid) |
API key |
Yes |
★★★★★ |
~90%+ |
Per plan |
Confidence Weighting
When merging data from multiple sources, apply confidence weights to each metric:
| Source |
Weight |
Rationale |
| DataForSEO |
1.00 |
Commercial-grade, real-time, comprehensive |
| Verification Crawler |
0.95 |
Direct observation (binary: link exists or not) |
| Moz API |
0.85 |
Large index (45.5T links), established metrics, 3-day update lag |
| Bing Webmaster |
0.70 |
Smaller index (~15% of web), but authoritative for Bing-indexed pages |
| Common Crawl |
0.50 |
Domain-level only, quarterly updates, no anchor text |
Composite formula:
weighted_score = Σ(source_score × confidence × factor_weight) / Σ(confidence × factor_weight)
When only Common Crawl is available, cap the maximum health score at 70/100 and note
"limited to domain-level metrics" in the report.
Source Details
Moz API (Tier 1)
- Endpoint:
https://api.moz.com/jsonrpc (JSON-RPC 2.0)
- Free tier: 2,500 rows/month, 1 request per 10 seconds (verify current limits at https://moz.com/products/api — free tier limits may change)
- Signup: https://moz.com/products/api (credit card required, not charged)
- Data: Domain Authority (0-100), Page Authority, Spam Score (1-17%), link counts,
referring domains, anchor text distribution
- Script:
scripts/moz_api.py
- Commands:
metrics, domains, anchors, pages
- Blind spots: No link velocity, no toxic link patterns beyond Spam Score,
3-day update lag, smaller index than Ahrefs/Semrush
- Endpoint:
https://ssl.bing.com/webmaster/api.svc/json/
- Free tier: Unlimited for verified sites
- Signup: https://www.bing.com/webmasters (Microsoft account)
- Comparison: Backlink-domain gaps between two registered properties that
are accessible to the same API account
- Data: Inbound-link source URL, target URL, anchor text, sampled link
counts, and referring-domain comparison totals
- Script:
scripts/bing_webmaster.py
- Commands:
links, counts, compare (comparison requires both
properties to be registered to the same API account)
- Blind spots: Only Bing-indexed pages (~15% of web), verified sites only,
no authority metrics, no spam scoring
Common Crawl Web Graph (Always Available)
- Data source:
s3://commoncrawl/projects/hyperlinkgraph/
- Releases: Quarterly (e.g., cc-main-2025-18)
- No auth needed: Public data, free to download
- Data: Domain-level in-degree, PageRank, harmonic centrality, referring domains
- Script:
scripts/commoncrawl_graph.py
- Cache:
~/.cache/claude-seo/commoncrawl/ (90-day TTL)
- Blind spots: No anchor text, no page-level data, monthly/quarterly freshness,
domain-level only (e.g., "nytimes.com links to example.com" but not which page)
Verification Crawler (Always Available)
- No auth needed: Uses existing fetch_page.py + parse_html.py
- Data: Binary verification (link exists/lost/moved), anchor text, rel attributes
- Script:
scripts/verify_backlinks.py
- Input: JSON file with
[{"source_url": "..."}] entries
- Polite crawling: 1-second delay between requests to same domain
- Best for: Checking if known backlinks still exist, monitoring link health
When to Recommend DataForSEO Upgrade
Suggest the paid DataForSEO extension when:
- User needs toxic link detection beyond Moz's basic Spam Score
- User needs competitor gap analysis at scale or against an unregistered
domain (Bing comparison is limited to properties accessible to the account)
- User needs link velocity trends (new/lost links over time)
- User needs real-time data (free sources update monthly at best)
- User manages multiple client sites (free tier limits are per-account)
- User needs disavow file generation with confidence scoring
Data Quality Reality Check
- Commercial tools index 35-45 trillion links across 500M+ referring domains
- Free sources combined capture 20-40% of raw backlink data
- But 60-70% of actionable intelligence since highest-authority links appear in free samples
- For sites with <500 backlinks, free sources can capture 50%+ of the meaningful profile
- Referring domain count matters more than raw backlink count for SEO
- Top 50-100 referring domains capture the majority of link authority
Five Systematic Biases in Free Data
- Popularity bias: Free tools crawl popular sites more, underrepresenting niche sites
- Truncation bias: All free tools cap at 100-1,000 links, hiding the long tail
- Own-site restriction: GSC and Ahrefs Webmaster Tools only work for verified properties
- Missing quality metrics: Raw CC data lacks authority/toxicity scores
- Freshness lag: Free sources update monthly at best vs. minutes for commercial