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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
Research depth
Discovery
How well the tool supports keyword, competitor, SERP, backlink, or market research before execution.
Semrush
Deep keyword, competitor, backlink, and domain research workflows are explicitly documented.
SEO Toolkit lists competitor research, Keyword Gap, Keyword Overview, Keyword Magic Tool, backlinks, and related reports: https://www.semrush.com/kb/806-seo-toolkit
Read the full reviews: Semrush 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.
Semrush
Keyword research is a core workflow with a large proprietary database and multiple dedicated tools.
Semrush cites its keyword database and lists Keyword Overview, Keyword Magic Tool, and Keyword Strategy Builder: https://www.semrush.com/kb/806-seo-toolkit
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.
Semrush
Content optimization is included in Pro+ and the platform documents briefs and draft scoring, but publishing is not core SEO-plan execution.
Pro+ includes content optimization; Semrush describes briefs and draft scoring: https://www.semrush.com/pricing/seo-ai-search/; https://www.semrush.com/kb/995-what-is-semrush
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.
Semrush
Competitor domains, traffic sources, top pages, keyword gaps, and backlink context are supported.
The official feature list describes domain strategy, traffic sources, top pages, keyword gaps, and backlinks: https://www.semrush.com/kb/995-what-is-semrush
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.
Semrush
Current plans track AI prompts, AI brand performance, sentiment, and visibility across major AI systems.
Pricing lists AI-search tracking and AI Visibility limits; the product page names ChatGPT, Gemini, and Perplexity: https://www.semrush.com/pricing/seo-ai-search/; https://www.semrush.com/kb/995-what-is-semrush
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.
Semrush
Multi-location and device tracking is explicitly available in Pro+.
Pro+ includes multi-location/device tracking: https://www.semrush.com/pricing/seo-ai-search/
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.
Semrush
Site Audit and on-page/technical SEO workflows are core SEO Toolkit capabilities.
The Toolkit lists Site Audit, On Page SEO Checker, and technical SEO auditing: https://www.semrush.com/kb/806-seo-toolkit
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.
Semrush
Official pages support content optimization and describe content workflows, but do not establish a full native publishing workflow for the core product.
The core pricing page only explicitly lists content optimization at Pro+; the official product description discusses content workflows without establishing core CMS publishing: https://www.semrush.com/pricing/seo-ai-search/; https://www.semrush.com/kb/995-what-is-semrush
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.
Semrush
Daily keyword rank tracking, AI visibility reporting, sentiment monitoring, and SEO Share of Voice are supported.
SEO, Pro+, and Advanced plan features include Position Tracking, AI reports, sentiment, and Share of Voice: https://www.semrush.com/pricing/seo-ai-search/
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.
Semrush
Team/agency positioning and additional-user support exist, but advanced collaboration is primarily enterprise-oriented.
Semrush describes plans for teams/agencies and additional-user pricing, while enterprise adds team governance: https://www.semrush.com/kb/1011-subscriptions
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.
Semrush
A free tier and trials make evaluation accessible, but paid plans start at a high monthly price.
Free is $0 and seven-day trials are documented; SEO is $139 monthly: https://www.semrush.com/pricing/seo-ai-search/; https://www.semrush.com/kb/1011-subscriptions
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.
Semrush
A limited free account exists with one demo project and daily report limits.
The official pricing page states the Free plan limits: https://www.semrush.com/pricing/seo-ai-search/
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.
Semrush
Official company materials provide meaningful adoption figures, though the clearest paying-customer figure is from 2023.
Company timeline reports 100,000 paying customers and 1,000,000 free registered active users in 2023: https://www.semrush.com/company/
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.
Semrush
MCP access and API data integration provide machine-access paths, but the evidence does not establish a broadly autonomous SEO agent.
Starter includes MCP access and Advanced includes API data integration: https://www.semrush.com/pricing/seo-ai-search/
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.
Semrush
AI-powered recommendations and AI visibility features assist workflows, but human execution remains necessary.
Semrush describes AI-powered recommendations and AI visibility features, while the SEO Toolkit presents actionable insights rather than autonomous execution: https://www.semrush.com/kb/1011-subscriptions; https://www.semrush.com/kb/806-seo-toolkit
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