Locust vs Percy

Locust is an open-source performance and load testing tool for HTTP and other protocols. Test scenarios are written in Python, with regular Python libraries available for use within them. Tests can run from the command line or web interface, which displays throughput, response times, and errors in real time; results can be exported for later analysis. The interface shows progress and lets users change load during a run. Locust can distribute tests across multiple machines and says it can support hundreds of thousands of concurrent users. Other systems and protocols can be tested by adding a client, and documentation lists community extensions for protocols and reporting. Optional OpenTelemetry support exports traces, metrics, and logs to compatible backends such as OTLP, Prometheus, Jaeger, and Tempo. Automatic instrumentation currently covers the requests library. Installation is documented with pip install locust or uvx. Locust is free and MIT-licensed. Its documentation also describes hosted load testing through Azure Load Testing, with reporting, Application Insights integration, and CI/CD support for Azure DevOps and GitHub Actions.

Percy automates visual testing by capturing DOM snapshots and assets, rendering them across browsers, and comparing results with earlier snapshots to flag visual changes. Responsive checks use configurable widths, while snapshot stabilization freezes animations and other dynamic elements to reduce false positives. Percy groups snapshots into the same build when tests run in separate processes or on different machines. Its review workflow includes status updates, notifications, comments, comparisons, and automatic diff matching. Listed integrations include GitHub, GitLab, Slack, Storybook, WebdriverIO, and Jenkins. Documented frameworks include Selenium, Playwright, Cypress, Puppeteer, Ember, Appium, and others. Percy documentation describes testing across real devices and desktop and mobile browsers. The free plan includes 5,000 screenshots per month, unlimited users, and unlimited projects. Desktop costs $199 a month, billed annually, for 10,000 screenshots per month; Desktop & Mobile costs $599 a month, billed annually, for 25,000 screenshots per month. Paid plans have fixed screenshot allowances, and additional usage is charged at the overage rate. Enterprise pricing is custom and unlisted.