All four generate load and give the same results, p95, error rate and so on. The difference is who writes the test and how, where the load comes from and how the result is shared with the team. Spitfire is a self-hosted platform with a web UI, for a team; the others are mostly tools a developer runs on their own machine.
| Spitfire | k6 | JMeter | Locust | |
|---|---|---|---|---|
| To write a test | Web editor or JSON | JavaScript | Desktop GUI | Python |
| Single sign-on (OIDC, LDAP) | ✓ group → role mapping | — cloud edition | — | — |
| Self-hosted team UI | ✓ roles, groups | — cloud edition | — | ~ no users |
| SQL · Kafka · MQTT · Redis · MongoDB | ✓ built in | ~ extensions | ~ partly | ~ in code |
| Several locations in one run | ✓ by percent | — cloud edition | ~ manual | ~ manual |
| Tests from OpenAPI / Postman / HAR | ✓ in the UI, auto-correlation | ~ separate converters | ~ recording proxy, plugins | — |
| Production write guard | ✓ | — | — | — |
| Shareable report | ✓ PDF, HTML, link | ~ HTML only | ~ HTML only | ~ HTML only |
| Scheduled runs + Slack / Teams / e-mail | ✓ built in, PDF attached | — cloud edition | ~ via a CI server | — |
| Alert on a regression against the baseline | ✓ Slack, Teams, e-mail, webhook | — | — | — |
| Responses of failed requests | ✓ samples on the run page | ~ by logging in code | ~ with a listener | ~ error text only |
| Audit log | ✓ tamper-proof | — | — | — |
| Pass/fail exit code for CI | ✓ k6-compatible, on your runners | ✓ | ~ | ✓ |
Compared against each tool's open-source edition.
Grafana k6 is open source (AGPL-3.0); tests are written in JavaScript and run from a single binary. HTTP, WebSocket and gRPC are built in; protocols like Kafka or SQL need a custom build with xk6 extensions. The open-source edition has no multi-location runs, team UI or scheduled runs; those are in Grafana Cloud k6. In Spitfire, threshold expressions (p(95)<500, rate<0.01) and CI exit codes are the same as k6's, so the gate in your pipeline stays. A k6 script is not imported directly; you turn the same API into a test from OpenAPI, Postman or a browser recording in minutes. If you need page metrics in a real browser (k6 browser), k6 fits better: Spitfire generates load at the protocol level.
Apache JMeter is open source (Apache 2.0) and runs on Java; the test plan is built in a desktop GUI and saved as .jmx (XML), and load runs are recommended without the GUI. Its protocol range is very wide: HTTP, JDBC, JMS, LDAP, FTP, SMTP, TCP and plugins. In a distributed run the main machine connects to remote servers, so the load servers need an inbound port open. In Spitfire the test is built in the browser and versioned as JSON, runners dial out to the controller, and the result shows live during the run. If you need JMS, LDAP or FTP load, JMeter fits better.
Locust is open source (MIT); tests are Python code, and a web UI starts the run and follows it live. HTTP is built in; other protocols need a Python client written for them. In a distributed run the workers connect to the main process. Spitfire needs no code: steps, extraction, checks and thresholds are in the UI; Kafka, SQL, MQTT, Redis, MongoDB and gRPC are ready, and there are users, roles and an audit log. If you want to program every virtual user's behaviour freely in Python, Locust fits better.
The free edition limits scale, not features. Install it with one command (installation guide) and start from an example or your own OpenAPI document.
Compared against each tool's open-source edition and its own documentation (September 2026). If you see something wrong or out of date, tell us and we will fix it.