Sill vs SearchPilot: GEO Experimentation Compared
Read the postDateApr 5, 2026
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SEOTesting added an LLM test type that tracks GA4 sessions from AI chatbots before and after on-site changes. Sill measures AI citations directly across six platforms with statistical controls. These tools answer different questions using different data sources, and understanding the distinction matters for teams choosing where to invest measurement budget.
TL;DR
SEOTesting ($50-$375/mo) is the only tool with an explicit LLM test type, measuring GA4 sessions from AI chatbots before and after page changes. Their documentation acknowledges the limitation: it is not always obvious how or when content gets included in LLM answers. GA4 misses over 70% of AI traffic because platforms strip referrer headers. Sill (Free-$225/mo) measures AI citation shifts directly across six platforms using statistical controls, with per-platform models and calibration for empirical false positive rates. SEOTesting measures what GA4 can capture; Sill measures what AI platforms actually say. SEOTesting is the most accessible entry point at $50/mo for teams that want any LLM signal from existing analytics. Sill is built for teams that need to measure whether content changes shifted AI citations across ChatGPT, Perplexity, Gemini, Google AI Overviews, Claude, and Grok.
SEOTesting tracks LLM referral sessions in GA4 ($50-$375/mo); Sill measures direct AI citation shifts across 6 platforms (Free-$225/mo).
SEOTesting ($50-$375/mo) is an SEO testing platform built on Google Analytics and Search Console data. It offers multiple test types for measuring the impact of on-site changes on organic performance. Its LLM test type is the feature relevant to this comparison: it measures GA4 sessions attributed to AI chatbot referrals before and after a page change. The tool integrates with GA4 and Google Search Console, requires no traffic minimum, and provides a straightforward before-and-after comparison.
Sill (Free-$225/mo) monitors brand mentions across ChatGPT, Perplexity, Gemini, Google AI Overviews, Claude, and Grok. Rather than relying on analytics referral data, Sill queries AI platforms directly to track whether and how each platform mentions your brand. The experimentation layer uses statistical controls to measure whether content changes shifted citation patterns, fitting models independently per platform and using calibration to establish empirical false positive rates. All six platforms are included at every pricing tier.
SEOTesting's LLM test measures GA4 sessions from AI chatbots using before-and-after comparison; GA4 misses over 70% of AI traffic due to stripped referrer headers.
SEOTesting's LLM test type tracks sessions from ChatGPT, Claude, and Perplexity using GA4 referral data. The methodology is time-based: select the date when a change was made, then compare sessions from AI chatbot referrals in the period before versus the period after. Their own documentation is transparent about the constraint: "LLM answers are generated from a mix of sources, and it's not always obvious how or when your content gets included."
The fundamental limitation is the data source. GA4 captures AI traffic only when the referrer header is intact. Most AI platforms strip referrer headers before sending users to destination sites. Independent research estimates GA4 misses over 70% of AI-originated visits. The visible fraction is real and worth measuring, but it represents a minority of actual AI-driven traffic.
At $50/mo with no traffic minimums, SEOTesting is the most accessible tool for teams that want any LLM traffic signal from their existing analytics stack. The value proposition is clear: low cost, simple setup, immediate signal from a data source the team already has. It should be understood as directional measurement of a partial signal, which SEOTesting itself acknowledges.
SEOTesting measures GA4 referral traffic from AI chatbots; Sill queries AI platforms directly to measure citation presence and shifts.
The tools operate at different layers of the measurement stack. SEOTesting measures downstream traffic: did AI chatbot users click through to your page? Sill measures upstream citations: did AI platforms mention your brand in their answers?
| Dimension | SEOTesting | Sill |
|---|---|---|
| Data source | GA4 referral sessions | Direct AI platform queries |
| Methodology | Before-and-after time comparison | Statistical controls (affected vs. unaffected prompts) |
| AI platforms | Whatever GA4 captures (ChatGPT, Claude, Perplexity referrals) | 6 dedicated: ChatGPT, Perplexity, Gemini, AI Overviews, Claude, Grok |
| Pricing | $50-$375/mo | Free-$225/mo (6 platforms at every tier) |
| What it proves | Traffic correlation: AI referral sessions changed after a page edit | Citation shifts: AI platforms mention your brand differently after a content change |
| Traffic minimum | None (GA4 integration required) | None (25+ prompts for experimentation) |
| AI traffic coverage | Partial: only sessions with intact referrer headers | Full: queries platforms directly regardless of referrer |
SEOTesting for budget-conscious teams wanting any LLM traffic signal from GA4; Sill for teams wanting direct AI citation measurement across six platforms.
Choose SEOTesting if you are on a tight budget, already use GA4, and want to see whether AI chatbots are driving any measurable traffic to your pages. At $50/mo, the barrier is low and the setup is straightforward. The LLM test type gives you a directional signal from data you already collect. The limitation is that GA4 captures a fraction of actual AI-originated visits, and before-and-after comparison cannot isolate whether a content change or an external factor (model update, competitor movement, citation source rotation) caused the traffic shift.
Choose Sill if you need to measure what AI platforms are saying about your brand, not just whether AI users clicked through. Direct citation measurement across six platforms, statistical controls for separating signal from noise, and GEO recommendations for acting on the results. Sill's free tier includes monitoring across all 6 AI platforms, GEO recommendations, and Brand Watchdog. Experimentation requires 25+ prompts, available from the $90/mo Basic plan.
The two tools can be complementary. SEOTesting tells you whether AI traffic is reaching your pages; Sill tells you whether AI platforms are mentioning your brand. A team running both gets downstream traffic data and upstream citation data, covering more of the measurement gap than either tool alone.
For the full landscape of GEO testing and experimentation tools, see our hub comparison of every GEO testing tool in 2026.
Sill monitors your brand across ChatGPT, Perplexity, Gemini, Google AI Overviews, Claude, and Grok. Free tier includes all six platforms.
Request your first analysis today to see where you stand.