SEO Drift Monitor (April 2026)

Git for your SEO. Capture baselines, detect regressions, track changes over time.

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Commands

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What It Captures

Every baseline records these SEO-critical elements:

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How Comparison Works

The comparison engine applies 17 rules across 3 severity levels. Load references/comparison-rules.md for the full rule set with thresholds, recommended actions, and cross-skill references.

Severity Levels

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Storage

All data is stored locally in SQLite:

~/.cache/claude-seo/drift/baselines.db

Tables

• baselines: Captured snapshots with all SEO elements
• comparisons: Diff results with triggered rules and severities

URL normalization ensures consistent matching: lowercase scheme/host, strip default ports (80/443), sort query parameters, remove UTM parameters, strip trailing slashes.

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Command: baseline

Captures the current state of a page and stores it.

Steps:

1. Validate URL (SSRF protection via google_auth.validate_url())
2. Fetch page via scripts/fetch_page.py
3. Parse HTML via scripts/parse_html.py
4. Optionally fetch CWV via scripts/pagespeed_check.py (use --skip-cwv to skip)
5. Hash HTML body and schema content (SHA-256)
6. Store snapshot in SQLite

Execution:

python3 scripts/drift_baseline.py <url>
python3 scripts/drift_baseline.py <url> --skip-cwv

Output: JSON with baseline ID, timestamp, URL, and summary of captured elements.

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Command: compare

Fetches the current page state and diffs it against the most recent baseline.

Steps:

1. Validate URL
2. Load most recent baseline from SQLite (or specific --baseline-id)
3. Fetch and parse current page state
4. Run all 17 comparison rules
5. Classify findings by severity
6. Store comparison result
7. Output JSON diff report

Execution:

python3 scripts/drift_compare.py <url>
python3 scripts/drift_compare.py <url> --baseline-id 5
python3 scripts/drift_compare.py <url> --skip-cwv

Output: JSON with all triggered rules, old/new values, severity, and actions.

After comparison, offer to generate an HTML report:

python3 scripts/drift_report.py <comparison_json_file> --output drift-report.html

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Command: history

Shows all baselines and comparisons for a URL.

Execution:

python3 scripts/drift_history.py <url>
python3 scripts/drift_history.py <url> --limit 10

Output: JSON array of baselines (newest first) with timestamps and comparison summaries.

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Cross-Skill Integration

When drift is detected, recommend the appropriate specialized skill:

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Error Handling

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Security

• All URL fetching goes through scripts/fetch_page.py which enforces SSRF protection (blocks private IPs, loopback, reserved ranges, GCP metadata endpoints)
• No curl, no subprocess HTTP calls -- only the project's validated fetch pipeline
• All SQLite queries use parameterized placeholders (?), never string interpolation
• TLS always verified -- no verify=False anywhere in the pipeline

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Typical Workflows

Pre/Post Deployment Check

/seo drift baseline https://example.com     # Before deploy
# ... deploy happens ...
/seo drift compare https://example.com      # After deploy

Ongoing Monitoring

/seo drift baseline https://example.com     # Initial capture
# ... weeks later ...
/seo drift compare https://example.com      # Check for drift
/seo drift history https://example.com      # Review all changes

Investigating a Traffic Drop

/seo drift compare https://example.com      # What changed?
/seo drift history https://example.com      # When did it change?

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Supporting file: references/comparison-rules.md

SEO Drift Comparison Rules

17 rules across 3 severity levels. Each rule compares a specific SEO element between the stored baseline and the current page state.

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CRITICAL (Immediate Action Required)

These changes typically cause measurable traffic loss within days.

Rule 1: Schema/JSON-LD Completely Removed

• Compare: Baseline schema array has items, current is empty
• Threshold: Any schema present before, none now
• Action: Restore structured data immediately. Rich results will be lost within hours.
• Cross-ref: /seo schema <url>

Rule 2: Canonical URL Changed

• Compare: Baseline canonical vs current canonical
• Threshold: Different non-null values (after normalization)
• Action: Verify the new canonical is intentional. Incorrect canonicals redirect ranking signals to wrong page.
• Cross-ref: /seo technical <url>

Rule 3: Canonical URL Removed

• Compare: Baseline canonical was set, current is null
• Threshold: Had value, now missing
• Action: Restore canonical tag. Google will guess, often incorrectly for pages with query parameters.
• Cross-ref: /seo technical <url>

Rule 4: Noindex Directive Added

• Compare: Baseline meta_robots did not contain "noindex", current does
• Threshold: "noindex" substring now present (case-insensitive)
• Action: If unintentional, remove immediately. Page will be dropped from index within days.
• Cross-ref: /seo technical <url>

Rule 5: H1 Tag Removed Entirely

• Compare: Baseline h1 had entries, current is empty
• Threshold: One or more H1s before, zero now
• Action: Restore H1 heading. Primary page topic signal for search engines.
• Cross-ref: /seo content <url>

Rule 6: H1 Text Changed Significantly

• Compare: First H1 in baseline vs first H1 in current, SequenceMatcher ratio
• Threshold: Similarity ratio < 0.5 (>50% different)
• Action: Verify the H1 change aligns with target keyword strategy.
• Cross-ref: /seo content <url>

Rule 7: Title Tag Removed Entirely

• Compare: Baseline title was set, current is null or empty
• Threshold: Had value, now missing
• Action: Restore title tag immediately. Google will auto-generate one, often poorly.
• Cross-ref: /seo page <url>

Rule 8: HTTP Status Code Changed to Error

• Compare: Baseline status_code was 2xx, current is 4xx or 5xx
• Threshold: Status code class changed from success to client/server error
• Action: Investigate server error or missing page. Rankings will drop within days.
• Cross-ref: /seo technical <url>

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WARNING (Investigate Within 1 Week)

These changes may impact rankings or CTR but are sometimes intentional.

Rule 9: Title Text Changed

• Compare: Baseline title vs current title (trimmed)
• Threshold: Strings differ (case-sensitive, whitespace-normalized)
• Action: Verify new title includes target keywords. Monitor CTR in GSC over 2 weeks.
• Cross-ref: /seo page <url>

Rule 10: Meta Description Changed

• Compare: Baseline meta_description vs current meta_description
• Threshold: Strings differ (trimmed)
• Action: Verify new description includes call-to-action and target keywords. Monitor CTR.
• Cross-ref: /seo page <url>

Rule 11: Core Web Vitals Metric Regressed >20%

• Compare: Each CWV metric p75 value (LCP, INP, CLS) baseline vs current
• Threshold: Current value is >20% worse than baseline (higher for LCP/INP, higher for CLS)
• Action: Investigate performance regression. Check recent code changes or third-party scripts.
• Cross-ref: /seo technical <url>

Rule 12: CWV Performance Score Dropped 10+ Points

• Compare: Lighthouse performance score baseline vs current
• Threshold: Drop of 10 or more points (e.g., 85 to 74)
• Action: Run full PageSpeed analysis to identify new bottlenecks.
• Cross-ref: /seo google psi <url>

Rule 13: OG Tags Removed

• Compare: Baseline open_graph had entries, current is empty
• Threshold: One or more OG tags before, none now
• Action: Restore OG tags. Social sharing will show generic/missing previews.
• Cross-ref: /seo page <url>

Rule 14: Schema/JSON-LD Content Modified

• Compare: Baseline schema_hash vs current schema_hash
• Threshold: Hash differs AND schema still exists (removal is Rule 1)
• Action: Validate modified schema. Check for type changes, removed properties, or new validation errors.
• Cross-ref: /seo schema <url>

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INFO (Awareness Only)

These are tracked for completeness. Often positive or neutral changes.

Rule 15: New Schema/JSON-LD Added

• Compare: Baseline schema was empty, current has items
• Threshold: No schema before, schema now present
• Action: Positive change. Validate the new schema with /seo schema <url>.
• Cross-ref: /seo schema <url>

Rule 16: H2 Structure Changed

• Compare: Baseline h2 array vs current h2 array
• Threshold: Different number of H2s, or different H2 text values
• Action: Review heading hierarchy. Ensure content sections still align with target topics.
• Cross-ref: /seo content <url>

Rule 17: Content Hash Changed

• Compare: Baseline html_hash vs current html_hash
• Threshold: Hash differs (catch-all for any body content change)
• Action: General content change detected. Review if no other rules triggered to understand what changed.
• Cross-ref: /seo page <url>