Loading page
Tool comparison
Both tools graded on the same fifteen criteria. The verdict lists the criteria where one tool leads the other by two points or more.
Verdict
Verdict
These tools solve different jobs. Scores are shown against each tool's own category, so the overall grades are not directly comparable. How grades work.
Research depth
Discovery
How well the tool supports keyword, competitor, SERP, backlink, or market research before execution.
Similarweb
Deep multi-surface market and digital intelligence.
Website, app, keyword, company, technology and audience data are exposed through products and APIs. https://www.similarweb.com/corp/daas/api/
Read the full reviews: Similarweb and WebPageTest.
WebPageTest
Deep page-performance diagnosis, but no keyword, SERP, competitor, backlink, or market research workflow.
WebPageTest diagnoses DNS, TCP, TLS, loading, rendering, and Core Web Vitals for tested pages. https://www.webpagetest.org/
Keyword research quality for SEO content
Discovery
How well the tool identifies, qualifies, clusters, and prioritizes keywords specifically for SEO content creation.
Similarweb
Fresh granular keyword discovery and competitive analysis.
The SEO suite describes high-intent discovery, emerging 28-day trends, keyword research and competitor gaps. https://www.similarweb.com/corp/teams/seo/
WebPageTest
No keyword discovery or keyword-volume workflow is documented.
The official product pages describe performance tests, Core Web Vitals, and diagnostics, but provide no keyword-research feature. https://www.webpagetest.org/
Content execution
Execution
How well the tool helps produce, optimize, or operationalize SEO content.
Similarweb
Strong planning and recommendations; limited editorial production evidence.
The agent recommends formats, structures, on-page elements and content to create or optimize. https://www.similarweb.com/corp/ai/agents/seo-strategist/
WebPageTest
No content briefing, generation, or optimization workflow is documented.
The pricing feature list covers testing, Lighthouse, Opportunities, scripts, API, and Experiments, not content execution. https://www.webpagetest.org/signup
Context gathering
Grounding
How well the tool gathers the business, competitor, SEO, internal, third-party, and custom API context needed for differentiated recommendations and content.
Similarweb
Exceptional competitor, audience, market, SERP and source context.
Competitive analysis, demographics, channels, keywords and AI citations are combined. https://www.similarweb.com/packages/ai-search/
WebPageTest
Grounded in detailed page-load, browser, network, device, and CrUX data, not business or broad SEO context.
Users configure browser, region, device, and connection for performance tests and can compare lab and field metrics. https://www.webpagetest.org/webvitals
AI-search / GEO
Visibility
How directly the tool helps teams improve visibility in AI answer engines and citation-oriented search journeys.
Similarweb
Dedicated generative-AI visibility measurement.
AI Brand Visibility reports mentions, prompts, citations, sentiment, topics and competitors. https://www.similarweb.com/corp/search/gen-ai-intelligence/ai-brand-visibility/
WebPageTest
No generative-engine optimization feature is documented.
The official pages mention SEO rankings via Core Web Vitals but do not claim generative-search visibility, citation tracking, or AI-search optimization. https://www.webpagetest.org/
GEO readiness
Visibility
How ready the tool is for generative engine optimization: answer-engine visibility, citation likelihood, AI-search prompt surfaces, and content structures that AI systems can use.
Similarweb
Strong GEO diagnosis; less evidence of automatic remediation.
Source-level citations, prompt gaps, topic and sentiment views support generative-engine optimization. https://www.similarweb.com/corp/search/gen-ai-intelligence/ai-brand-visibility/
WebPageTest
No GEO capability in the generative-optimization sense.
The location capabilities are for performance testing geography, not generative-engine optimization. https://www.webpagetest.org/webvitals
Technical SEO
Diagnostics
How strong the tool is for crawling, audits, indexability, metadata, status codes, and technical site health.
Similarweb
Full technical SEO audit and site-health workflow.
Site Audit crawls complex sites and analyzes 300+ performance factors. https://www.similarweb.com/corp/search/site-audit/
WebPageTest
Very strong Core Web Vitals and page-performance diagnostics.
The homepage explicitly connects WebPageTest to Core Web Vitals and SEO rankings; Tips also lists CrUX, Lighthouse, in-depth metrics, waterfalls, and API/integrations. https://www.webpagetest.org/tips.php
Publishing workflow
Operations
How well the tool moves work into CMS, publishing, approvals, or automated production workflows.
Similarweb
Planning is strong but publishing workflow is lightly documented.
SEO team copy says agents can publish content, while detailed agent page centers on recommendations. https://www.similarweb.com/corp/teams/seo/
WebPageTest
No CMS, editorial calendar, or publishing integration is documented.
The documented integrations are performance-testing/CI workflows rather than publishing workflows. https://www.webpagetest.org/tips.php
Measurement & tracking
Measurement
How well the tool monitors rankings, content performance, visibility, or ongoing SEO progress.
Similarweb
Daily rank, AI visibility, citation, sentiment, traffic and reporting coverage.
Rank tracking and AI Brand Visibility provide daily trends and ongoing visibility metrics. https://www.similarweb.com/corp/search/seo/
WebPageTest
Strong measurement, history, comparisons, and monitoring options.
Starter includes 60 days of history and Professional 13 months, while Professional adds scheduled tests, alerts, dashboards, and monitoring-oriented features. https://www.webpagetest.org/signup
Team collaboration
Operations
How well the tool fits multi-person workflows, agencies, approvals, handoffs, and repeatable processes.
Similarweb
Dashboards, reporting, integrations and SSO aid teams; self-service is single-user.
Pricing lists custom dashboards, advanced reporting, integrations and SSO; plans specify 1 user. https://www.similarweb.com/pricing/
WebPageTest
Team seats, Slack results, and pull-request comments support engineering handoffs, without a broad SEO approval workflow.
WebPageTest documents Pro team members, Slack result sharing, and GitHub pull-request comments. https://www.webpagetest.org/tips.php
Value accessibility
Buying
How easy it is for a team to reach value relative to pricing, setup complexity, and required expertise.
Similarweb
Free entry points and transparent entry plans, but depth/API are paid.
AI Search publishes three prices; free data is high-level and paid drilldowns are deeper. https://www.similarweb.com/packages/ai-search/
WebPageTest
The core speed test is free and can run without an account.
The web-vitals page says users can run a free website speed test with no account, and Starter is listed at $0. https://www.webpagetest.org/webvitals
Free tools
Buying
How useful the tool is before payment through free tools, free plans, trials, or public utilities.
Similarweb
Several useful free tools, constrained versus paid intelligence.
Free Keyword Generator and Website Traffic Checker are published; free data is high-level. https://www.similarweb.com/generator/
WebPageTest
Free tier includes substantial analysis rather than only a teaser.
Starter includes 150 monthly runs, Lighthouse, Opportunities, Filmstrip and Video, custom scripts, 30 locations, and Carbon Control. https://www.webpagetest.org/signup
Estimated customer scale
Market proof
Estimated customer or user scale based on public claims, with source claims stored separately for auditability.
Similarweb
Official materials indicate major enterprise and overall scale.
Similarweb states 10,000+ customers and 200+ Fortune 500 customers. https://www.similarweb.com/pricing/
WebPageTest
No numeric first-party customer count was found.
The homepage says it is trusted by top brands and shows logos, but does not state a numeric customer count. https://www.webpagetest.org/
Agent readiness level
Automation
How ready the product is to operate as or inside an AI agent workflow, based on tracked subcriteria for autonomy, controls, integrations, memory, and evaluation.
Similarweb
Dedicated SEO/business agents plus MCP; autonomy breadth still developing.
AI Agents and a Claude MCP connector provide agent-facing workflows and API-backed queries. https://www.similarweb.com/corp/ai/agents/seo-strategist/
WebPageTest
APIs, scripting, custom metrics, and CI automation make tests programmable, but no dedicated autonomous SEO agent is documented.
WebPageTest documents API-controlled tests, scripting, GitHub automation, and a Node wrapper. https://www.webpagetest.org/tips.php
Ease of use and autonomous level
Automation
How easy it is for a team to reach useful outcomes, and how much work the product can perform autonomously after setup.
Similarweb
Agents automate research and prioritization but appear supervised.
Agent accepts keywords/site/country and generates a prioritized plan; more workforce capabilities are marked coming soon. https://www.similarweb.com/corp/ai/agents/seo-strategist/
WebPageTest
Professional supports scheduled/automated testing and alerts, but not autonomous SEO decision-making.
Professional includes scheduled tests, customizable alerts, API access, and Experiments; the API material describes automation in CI/CD. https://www.webpagetest.org/signup