BreakTest

BreakTest is a modern, JMeter-compatible performance testing tool.

It started as an independent fork of Apache JMeter and continues the familiar JMX workflow with a leaner runtime, current protocols, better debugging, and a faster development loop. Existing JMeter test plans remain important, but BreakTest is not intended to be a frozen copy of JMeter.

Why BreakTest Exists

Apache JMeter gave the performance testing community a durable model: test plans, samplers, controllers, assertions, extractors, listeners, and a file format people can keep in version control.

BreakTest keeps that useful model and moves the runtime forward:

• lower memory and CPU pressure for large HTTP tests
• HTTP/2 and a modern HTTP client stack
• Java 21+ and virtual-thread support
• a more modern GUI with simple light/dark themes
• better GUI feedback while building, debugging, and repairing scripts
• safer loading of old plans and plugin-heavy JMX files
• AI-assisted scripting with Codex, Claude Code, opencode, and MCP workflows
• a source-available Community edition that can be scaled by BreakTest Enterprise when one machine is no longer enough

Compared with the upstream baseline this work has already shown about 50% lower memory usage, with CPU reductions around 20-50% depending on workload, test shape, and runtime conditions.

BreakTest And BreakTest Enterprise

BreakTest Community is the source-available desktop and runtime distribution. Organizations may use it to build, debug, validate, and run performance tests against systems operated for their own internal purposes, subject to the Community license and any release-specific Community Limits.

BreakTest Enterprise is the paid shell around scaled execution and analysis. It runs BreakTest, JMeter, and k6 tests across your own infrastructure with distributed load generators, realtime results, raw data retention, reports, SLO validation, team workflows, and AI-assisted analysis.

The source stays available for permitted Community use. Enterprise is for commercially licensed use and running it seriously at scale.

What Is New Compared With JMeter 5.6.3

BreakTest is based on the JMeter workflow, but it makes deliberate changes where that helps day-to-day performance engineering. The first public release is not just a rename: it includes protocol, runtime, GUI, AI scripting, debugging, and migration work that has landed across the BreakTest PR series.

Modern HTTP Runtime

• Apache HttpClient 5 is the active HTTP sampler path.
• HTTP/2 is first-class, including negotiated fallback, HTTP/2 preferred selection, async execution, connect-time reporting, and file upload fixes.
• HTTP/2 resource usage is lower: reactor threads are limited by default, client rebuilds are avoided when the same user continues, and parallel samplers reuse HTTP state deterministically.
• HTTP/2 closed-session retry handling covers common HC5 connection-closure failures without reusing dead multiplexed sessions.
• NTLM authentication works on the HttpClient 5 path, including variable resolution before async challenge callbacks.
• Modern response decoding includes gzip, deflate, Brotli, and Zstandard.
• Timeout errors are reported more clearly, with expected connect/response timeouts shown as concise messages instead of noisy stack traces.
• HttpClient 4 runtime jars are still bundled for legacy plugin compatibility, while the built-in HTTP Request sampler stays on the modern client path.

Lower Resource Usage

• Lazy response decompression avoids paying decompression cost unless response data is actually inspected.
• Response retention modes can store compressed data, discard successful bodies, keep only failing bodies, or retain checksums instead of full payloads.
• Lightweight test-plan cloning reduces per-thread object churn for large plans.
• Per-sample metadata is lazy, so rich diagnostics are only stored when listeners such as View Results Tree need them.
• Header merging, temporary property handling, and per-thread scratch buffers reduce hot-path allocations.
• Java 21+ and virtual threads are used where they reduce runtime overhead.

Controllers, Scheduling, And User Flow

• Parallel Controller models browser-like concurrent requests with bounded parallel sampler execution and HTTP state safeguards.
• Fork Controller runs a child branch asynchronously while the main virtual-user flow continues, sharing the same context and variables.
• Standard Thread Group can switch between closed and open workload models.
• Open model scheduling includes helper syntax, even-arrival scheduling, maximum active thread limits, and graph preview support.
• Closed model phases let you combine different ramp-up speeds, hold periods, and thread targets, making it possible to shape almost any closed workload model from one schedule.
• Thread Group pacing controls apply pacing between iterations.
• Runtime user variables are cleared on new iterations when same-user mode is disabled, while initial variables remain available.
• Pause and Resume are available in the GUI and in headless runs through the same UDP command port used for shutdown, stop, heap dump, and thread dump commands. This makes it possible to pause a schedule during ramp-up and hold the current load instead of ramping further. In closed model, active threads are kept as-is. In open model, new arrivals are paused and active threads finish naturally, so load drops while the schedule is paused.
• Shutdown is quicker because it no longer waits for timers to complete. It still waits for in-flight server responses, so active requests can finish cleanly.

GUI Workflow Improvements

• The GUI uses a cleaner FlatLaf-based look with simple light and dark themes, giving the desktop a more harmonized modern feel without changing the core workflow.
• Undo and redo are enabled for semantic test-plan changes such as add, delete, update, move, and search/replace operations.
• Large JMX files load in the background with a loading overlay.
• Optional fast GUI loading can skip expensive normalization with jmeter.gui.load.fast=true.
• JMX files with missing plugin elements can open with disabled placeholders instead of failing the whole load.
• Missing plugin placeholders are visible in the GUI and inert in non-GUI runs.
• Search can flag pre-processors, post-processors, assertions, timers, and config elements.
• Search results can be selectively removed with confirmation, so bulk cleanup is possible without deleting parent elements accidentally.
• GUI validation skips artificial transaction delay and pacing sleeps.

AI Scripting And Repair

• BreakTest can run AI-assisted script repair from the GUI or through local agent tooling.
• The agent workflow works with tools such as Codex, Claude Code, and opencode through BreakTest's MCP server and command-line helpers.
• AI repair can inspect a failing or incomplete test plan, run bounded validation, and apply concrete JMX edits instead of only suggesting changes.
• The repair flow can add extractors, parameterize dynamic values, improve correlations, add assertions, and professionalize recorded scripts so they are easier to maintain.
• GUI support highlights the changes made during repair, making it easier to review what was added, changed, or removed.
• Project-local AI knowledge can be stored with the test plan so recurring conventions, application details, and scripting assumptions travel with the work.

Scripting, Data, And Correlation

• If and While Controllers support structured condition rows with all/any matching, while legacy expression mode remains available for old plans.
• Loop and While Controllers expose clearer index behavior and exported index variable display.
• Transaction Controller has clearer measurement modes plus built-in delay and pacing options with fixed, random, and Gaussian modes.
• Boundary, CSS/HTML, Regex, XPath, XPath2, JSONPath, and JMESPath extractors can fail the sampler when no value is found.
• CSV Data Set can read records in random order while preserving header behavior.
• CSV preview shows the first variable assignments before running the test.
• JSR223/Groovy is the intended scripting direction; legacy BeanShell, BSF, JEXL2, Rhino JavaScript, and LogKit paths are removed.

Visual Debugging And Migration

• View Results Tree shows richer request/response diagnostics, endpoint data, HTTP/TLS metadata, cookies, variables, binary/text detection, and jump-to-source.
• Rendered response views and raw text response views have separate lifecycle handling, so switching renderers shows the expected data.
• BreakTest JMX saves origin metadata used by newer debugging tools.
• HAR-backed recorded exchange views can show recorded request and response data next to replayed samples.
• Recorded-vs-replayed diffs help debug HAR migration and HTTP/2 replay issues.
• Transaction child samples preserve source paths so recorded exchange diffs can still navigate to the right test element.
• HTTP/2 HAR replay strips unsupported hop-by-hop headers and normalizes request/status lines for clearer comparisons.
• Host-only cookie matching is stricter so cookies do not leak to unrelated hosts or subdomains.

Modernization Choices

BreakTest removes or de-emphasizes old paths that make the runtime harder to maintain. That includes legacy HTTP implementations, old scripting engines, LogKit, and RMI Remote Server style distributed execution.

For local use, run BreakTest directly. For distributed execution, use BreakTest Enterprise or another controlled orchestration layer rather than reviving the old Remote Server model.

Compatibility

BreakTest intentionally keeps many JMeter names in package names, properties, file formats, command internals, and Maven coordinates. This preserves compatibility with existing test plans, plugins, scripts, and integrations.

Some compatibility limits are intentional:

• plugins that depend on removed internals may need migration
• legacy scripting engines are not a long-term direction
• new BreakTest JMX features may not round-trip into old JMeter versions
• Java 21 or later is required

The goal is a better tool for current performance engineering, not perfect preservation of every old edge case.

Requirements

• Java 21 or later
• A JDK is recommended when recording HTTPS traffic because keytool is useful for certificate handling
• Optional protocol libraries, such as JDBC or JMS drivers, should be placed in lib or lib/opt as needed

Install And Run

Unpack the binary distribution, then start BreakTest from bin:

cd breaktest-2026.07.11/bin
./breaktest

On Windows:

breaktest.bat

For non-GUI execution:

./breaktest -n -t test-plan.jmx -l results.jtl

GUI updates

The GUI checks for a new stable GitHub release at most once every 24 hours. You can also check immediately with Help > Check for Updates. When a new version is available, an update button appears in the status bar. BreakTest downloads the binary release, verifies both its GitHub SHA-256 digest and its published SHA-512 checksum, installs it after the GUI exits, and then restarts.

Self-update is available from writable binary installations. Source checkouts are never modified by the updater. Updates preserve bin/user.properties, bin/system.properties, non-core plugins in lib/ext, and user-installed JARs such as JDBC/JMS drivers in lib or lib/opt. Set breaktest.update.enabled=false in user.properties to disable automatic checks, or change breaktest.update.interval_hours to adjust their frequency.

Some internal property names, package names, and artifact names still use jmeter for compatibility.

Build From Source

BreakTest uses Gradle and JVM toolchains.

Build and test:

./gradlew build

Create local bin and lib contents for development:

./gradlew createDist

Run the GUI through Gradle:

./gradlew runGui

Create release archives:

./gradlew clean :src:dist:distTar :src:dist:distZip -Prelease

Release versions are configured in gradle.properties:

breaktest.version=2026.07.11

Do not include -SNAPSHOT in that property. Gradle appends the snapshot suffix automatically unless the build is run with -Prelease or -Prc=<number>.

Documentation

Generated distribution documentation is included under docs/ in release archives and starts at docs/index.html.

Developer notes:

• CONTRIBUTING.md
• gradle.md
• SECURITY.md
• THREAT_MODEL.md

Security Model

BreakTest inherits JMeter's trusted-test-plan model. Treat JMX files as executable input: they can define scripts, load classes, call functions, read files, make network requests, and interact with systems reachable from the test runner.

Only open or run test plans you trust, or isolate them first. Report suspected BreakTest vulnerabilities privately as described in SECURITY.md. If an issue also affects upstream Apache JMeter, follow the Apache Software Foundation security process as well.

Relationship To Apache JMeter

BreakTest was forked from Apache JMeter:

• https://github.com/apache/jmeter
• https://gitbox.apache.org/repos/asf/jmeter.git

BreakTest is independent from The Apache Software Foundation. It is not affiliated with, endorsed by, or sponsored by The Apache Software Foundation.

Apache, Apache JMeter, JMeter, the Apache feather, and the Apache JMeter logo are trademarks or registered trademarks of The Apache Software Foundation. BreakTest uses those marks only to describe the origin of the fork and compatibility with Apache JMeter.

License

BreakTest-specific materials are licensed under the BreakTest Community Source License 1.0. This is a source-available license, not an Open Source license.

Community use is limited to testing systems operated by your own organization. Performance-testing service providers, load-testing platform providers, third-party testing, hosted or managed offerings, redistribution, reuse in other products or JMeter extensions, and circumvention of Community Limits require prior written permission or a commercial license from Breaking IT.

Commercial licensing requests may be sent to info@breakingit.nl.

BreakTest is a derivative work of Apache JMeter. Copyright and attribution notices for Apache JMeter and other third-party components are retained in the source tree and distribution notices. Those third-party materials, including Apache JMeter code, remain governed by their own licenses, including the Apache License, Version 2.0.

For legal and licensing information, see:

• LICENSE
• NOTICE

Cryptographic Software Notice

This distribution may include software that has been designed for use with cryptographic software. The country in which you reside may have restrictions on the import, possession, use, or re-export of encryption software. Before using encryption software, check your country's laws, regulations, and policies.

BreakTest interfaces with the Java Secure Socket Extension (JSSE) API to provide HTTPS support.

BreakTest interfaces, via Apache HttpClient, with the Java Cryptography Extension (JCE) API to provide authentication features such as NTLM.

BreakTest does not include an implementation of JSSE or JCE.

Thanks

BreakTest exists because Apache JMeter established a useful, open model for performance testing. Thank you to the Apache JMeter community and to everyone testing, reporting, fixing, and modernizing BreakTest from here.