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Locust

Open Source

Python-based load testing tool with code-as-test scenarios.

Visit websiteGitHub

Pricing

Free / Open source

Type

Automation

Languages

Python

// VERDICT

Reach for Locust when you want to write load scenarios as Python code, scale out across workers easily, and watch a live web UI. Skip it when you want a GUI (JMeter), a different language (k6/Gatling), or maximum single-machine throughput.

Best for

Defining load tests as plain Python - user behaviour is ordinary code, with an easy distributed mode and a live web UI, ideal for Python teams who want flexible, scriptable load.

Avoid when

You want a GUI/record tool, a non-Python language, or the absolute highest single-node throughput.

CI/CD fit

Locust CLI (headless) · GitHub Actions · GitLab CI · Jenkins · distributed workers

Languages

Python

Team fit

Python teams · Developer-owned load testing · Teams wanting code-defined user behaviour

Setup

Easy

Maintenance

Low

Learning

Beginner

Licence

Free / Open source

// BEST FOR

  • Writing load scenarios as ordinary Python code
  • An easy distributed mode (master + workers) to scale load
  • A live web UI showing requests, failures and response times
  • Flexible user behaviour with full programming-language power
  • Python teams wanting load tests in their own stack
  • Headless runs in CI alongside the interactive UI

// AVOID WHEN

  • You want a GUI / record-and-playback tool (JMeter)
  • Your team doesn't work in Python
  • You need maximum throughput from a single node (wrk/Gatling)
  • A managed enterprise platform is required (LoadRunner/NeoLoad)
  • You want a non-code, business-tester-friendly tool
  • You only need a quick one-off HTTP benchmark (wrk/Vegeta)

// QUICK START

pip install locust
# locustfile.py: class User(HttpUser) with @task methods
locust -f locustfile.py            # web UI, or --headless -u 100 -r 10 in CI

// ALTERNATIVES TO CONSIDER

ToolChoose it when
k6You want JS-based load tests with a high-performance engine.
GatlingYou want a JVM DSL with an efficient async engine.
Apache JMeterYou want a GUI/record-based tool with a plugin ecosystem.

// FEATURES

  • Python user-behaviour scripts
  • Distributed master/worker mode
  • Web UI for live results
  • Event-driven via gevent
  • Custom protocol support via plugins

// PROS

  • Easy to adopt for Python teams
  • Real Python code, not a DSL
  • Distributed scaling is straightforward
  • Live web UI is friendly for stakeholders

// CONS

  • Lower per-worker performance than k6 or Gatling
  • Reporting less detailed out of the box
  • GIL limits single-process throughput

// EXAMPLE QA WORKFLOW

  1. Install Locust (pip)

  2. Write a locustfile with user tasks in Python

  3. Model realistic wait times and behaviour

  4. Run with the web UI to explore, or headless for CI

  5. Scale with master/worker processes for higher load

  6. Gate CI on failure/threshold criteria