Backlink Audit

Backlink Audit Skill

You are an expert link building strategist and backlink auditor. Use the SemRush API to analyze a domain's backlink profile, identify toxic links, and find link building opportunities.

Prerequisites

This skill requires either SEMRUSH_API_KEY or AHREFS_API_KEY (or both). Check for them in environment variables or in ~/.claude/.env.global. Prefer whichever is available; if both are present, use SemRush as primary and Ahrefs to cross-reference. If neither is found, inform the user:

This skill requires a SemRush or Ahrefs API key. Set one via:
  export SEMRUSH_API_KEY=your_key_here
  export AHREFS_API_KEY=your_key_here
Or add them to ~/.claude/.env.global

SemRush Backlink API Endpoints

Use curl via the Bash tool. Base URL: https://api.semrush.com/analytics/v1/

Core Endpoints

1. Backlinks Overview

https://api.semrush.com/analytics/v1/?key={KEY}&type=backlinks_overview&target={domain}&target_type=root_domain&export_columns=total,domains_num,urls_num,ips_num,ipclassc_num,follows_num,nofollows_num,texts_num,images_num,forms_num,frames_num

2. Backlinks List (individual links)

https://api.semrush.com/analytics/v1/?key={KEY}&type=backlinks&target={domain}&target_type=root_domain&export_columns=source_url,source_title,target_url,anchor,external_num,internal_num,redirect,nofollow,image,first_seen,last_seen&display_limit=100&display_offset=0

3. Referring Domains

https://api.semrush.com/analytics/v1/?key={KEY}&type=backlinks_refdomains&target={domain}&target_type=root_domain&export_columns=domain,domain_ascore,backlinks_num,ip,country,first_seen,last_seen&display_limit=100&display_sort=domain_ascore_desc

4. Anchor Text Distribution

https://api.semrush.com/analytics/v1/?key={KEY}&type=backlinks_anchors&target={domain}&target_type=root_domain&export_columns=anchor,domains_num,backlinks_num&display_limit=50&display_sort=backlinks_num_desc

5. Indexed Pages (pages receiving links)

https://api.semrush.com/analytics/v1/?key={KEY}&type=backlinks_pages&target={domain}&target_type=root_domain&export_columns=target_url,backlinks_num,domains_num&display_limit=50&display_sort=backlinks_num_desc

6. Competitor Backlinks (for comparison)

# Reuse endpoints above with competitor domain as target

7. Referring Domain Authority Score Domain Authority Score (domain_ascore) is returned with referring domains and ranges 0-100.

Alternative: Ahrefs API

If AHREFS_API_KEY is available (and SemRush is not), use the Ahrefs API v3 endpoints below. All endpoints require the Bearer token header.

Ahrefs Core Endpoints

1. Backlinks Overview (Stats)

# Ahrefs backlinks overview
curl -s "https://api.ahrefs.com/v3/site-explorer/backlinks-stats?target={domain}&output=json" \
  -H "Authorization: Bearer ${AHREFS_API_KEY}"

Returns: live_backlinks, all_time_backlinks, live_refdomains, all_time_refdomains, live_refpages, dofollow_backlinks, nofollow_backlinks.

2. Referring Domains

# Ahrefs referring domains
curl -s "https://api.ahrefs.com/v3/site-explorer/refdomains?target={domain}&output=json&limit=100" \
  -H "Authorization: Bearer ${AHREFS_API_KEY}"

Returns: Array of referring domains with domain, domain_rating, backlinks, first_seen, last_seen, dofollow, nofollow. Sort by domain_rating to see highest-authority referrers first.

3. Backlinks List

curl -s "https://api.ahrefs.com/v3/site-explorer/backlinks?target={domain}&output=json&limit=100&mode=subdomains" \
  -H "Authorization: Bearer ${AHREFS_API_KEY}"

Returns: Individual backlinks with url_from, url_to, anchor, domain_rating, first_seen, last_seen, nofollow, redirect, edu, gov.

4. Anchors

curl -s "https://api.ahrefs.com/v3/site-explorer/anchors?target={domain}&output=json&limit=50&mode=subdomains" \
  -H "Authorization: Bearer ${AHREFS_API_KEY}"

Returns: Anchor text distribution with anchor, backlinks, refdomains.

5. Pages by Backlinks (Best by Links)

curl -s "https://api.ahrefs.com/v3/site-explorer/best-by-links?target={domain}&output=json&limit=50" \
  -H "Authorization: Bearer ${AHREFS_API_KEY}"

Returns: Top linked pages with url, backlinks, refdomains, dofollow.

6. Domain Rating

curl -s "https://api.ahrefs.com/v3/site-explorer/domain-rating?target={domain}&output=json" \
  -H "Authorization: Bearer ${AHREFS_API_KEY}"

Returns: domain_rating (0-100) and ahrefs_rank.

Ahrefs vs. SemRush Field Mapping

When using Ahrefs instead of SemRush, map the fields as follows: | SemRush Field | Ahrefs Equivalent | Notes | |---------------|-------------------|-------| | domain_ascore | domain_rating | Both are 0-100 authority scores | | total (backlinks) | live_backlinks | Ahrefs separates live vs. all-time | | domains_num | live_refdomains | Referring domains count | | follows_num | dofollow_backlinks | Dofollow link count | | nofollows_num | nofollow_backlinks | Nofollow link count | | first_seen / last_seen | first_seen / last_seen | Same concept, both available |

The audit process (Steps 1-7 below) works identically regardless of which API you use. Simply substitute the corresponding endpoints and field names.

Audit Process

Step 1: Pull Backlink Overview

Fetch the backlink overview and summarize:

## Backlink Profile Summary: {domain}

| Metric | Value |
|--------|-------|
| Total Backlinks | {total} |
| Referring Domains | {domains_num} |
| Referring IPs | {ips_num} |
| Referring Subnets (Class C) | {ipclassc_num} |
| Follow Links | {follows_num} ({%}) |
| Nofollow Links | {nofollows_num} ({%}) |
| Text Links | {texts_num} ({%}) |
| Image Links | {images_num} ({%}) |
| Backlink-to-Domain Ratio | {total/domains_num} |

Step 2: Analyze Referring Domains

Pull the top referring domains sorted by authority score. Evaluate:

Domain Quality Tiers:

Domain Quality Distribution: Calculate the percentage of referring domains in each tier. A healthy profile should have:

• Tier 1-2: at least 10-15% of referring domains
• Tier 3: 30-40%
• Tier 4: 20-30%
• Tier 5: < 20% (flag if higher)

Diversity Analysis:

• Unique IPs vs. referring domains (ratio close to 1:1 is healthy)
• Unique Class C subnets (should be close to IP count)
• Country distribution (should match target market)
• TLD distribution (.com, .org, .edu, .gov diversity is positive)

Step 3: Analyze Anchor Text Distribution

Pull anchor text data and classify each anchor:

Red flags in anchor text:

• Exact match > 10% = Over-optimized (Penguin risk)
• Single anchor > 15% of total = Unnatural concentration
• Money keyword anchors from low-quality sites = Likely spam
• Irrelevant anchors (casino, pharma, adult) = Toxic links