The term load testing or stress testing is used in different ways in the professional software testing community. Load testing generally refers to the practice of modeling the expected usage of a software program by simulating multiple users accessing the program concurrently.

Browser-level vs. protocol-level users

Historically, all load testing was performed with automated API tests that simulated traffic through concurrent interactions at the protocol layer (often called protocol level users or PLUs). With the advance of containers and cloud infrastructure, the option is now present to test with real browsers (often called browser level users or BLUs). Each approach has its merits for different types of applications, but generally, browser-level users will be more akin to the real traffic that a website will experience and provide a more realistic load profile and response time measurement. BLUs are certainly a more expensive way of running tests and cannot work with all types of applications, specifically those that are not accessible through a web browser like a desktop client or API-based application.

Load testing tools

Tool nameCompany nameLicenseTypePricingFocusNotes
Apache JMeterApache Software FoundationApache License 2.0LocalFreeJava desktop application for load testing and performance measurement.
BlazeMeterPerforce Software, IncProprietaryCloud-basedFree version, demo, paid plan, contact for pricingWebsite, web app, mobile, database, and other scenariosScalable load up to 200,000 concurrent simulated browser users from across eight geographical locations. Can also be used for integration and functional testing.
Blitz (discontinued in 2018)Spirent CommunicationsProprietaryCloud-basedTrial availableWebsites, mobile, and REST APIsIt allows to simulate of up to 50,000 simultaneous virtual users from different worldwide locations.
Flood (discontinued in 2024)Tricentis APAC Pty LtdProprietaryCloud-basedFree plan, paid plan, contact for pricingBrowser based load testing, APIs and protocol driven applicationsScalable load up to millions of concurrent users from all geographic regions available on AWS and Azure, plus on-premise deployments. Pricing is based on Virtual User Hours consumed each month.
GatlingGatling CorpApache License 2.0Local, cloud-basedFree version, demo, paid plan, contact for pricingJava web applicationsPortable HTML reports.
HammerDBGPLv3LocalFreeDatabasesDatabase load testing and benchmarking tool.
Loader.ioSendGrid, IncProprietaryCloud-basedFree plan, paid plan, contact for pricingWeb applications and API
LoadRunnerOpenTextProprietaryLocal, Cloud-basedFree community edition; other: demo, free trial, contact for pricingPrimarily used for executing large numbers of tests (or a large number of virtual users) concurrently. Can be used for unit and integration testing as well.
LoadUI (integrated now in ReadyAPI)SmartBear SoftwareEUPLLocalDemo availableCross-platform load testing tool, targeted mainly at web services. Integrates with soapUI.
Open sourceMIT LicenseLocal, cloud-basedFree, hosted paid version availablePython based framework with load tests expressed in regular code
Login VSILogin VSI, Inc.ProprietaryLocalDemo, contact for pricingVirtual windows desktops workloads
NeoLoadTricentisProprietaryLocal, cloud-basedFree trial, demo, contact for pricingWeb and mobileLoad can be generated from local agents or from the cloud.
OpenSTACYRANOGNU General Public License 2.0LocalFreeWeb serverUtilizes a distributed software architecture based on CORBA. OpenSTA binaries available for Windows.
Parasoft SOAtestParasoftProprietaryLocal, cloud-basedDemo, contact for pricingPerformance testing tool that verifies functionality and performance under load. Supports SOAtest tests, JUnits, lightweight socket-based components. Detects concurrency issues.
Rational Performance TesterIBMProprietaryLocal, cloud-basedContact for pricingEclipse-based large-scale performance testing tool primarily used for executing large volume performance tests to measure system response time for server-based applications.
SiegeOpen sourceGPLv3 or laterLocalFreeWeb serversSupports basic authentication, cookies, HTTP, HTTPS and FTP protocols.
Silk PerformerMicro FocusProprietaryLocal, cloud-basedFree trial, contact for pricingApplication performance tool with cloud and local virtual agents. Supports most protocols and applications. Licensed.
SoapUISmartBear SoftwareEUPL Version 1.1LocalFree
Test StudioProgress TelerikProprietaryLocalFree trial, demo, paid planAssess how the website would perform if visited by a large number of users at the same time.
TsungOpen SourceGPL-2.0LocalFreeWeb servers, Databases, XMPPIt can be used to stress HTTP, WebDAV, SOAP, PostgreSQL, MySQL, LDAP, MQTT and Jabber/XMPP servers.
Visual Studio Enterprise edition (deprecated after Visual Studio 2019)MicrosoftProprietaryLocalPaid planVisual Studio Enterprise edition includes a load test tool that enables a developer to execute a variety of tests (web, unit, etc...) with a combination of configurations to simulate real user load. Microsoft announced[when?] that its web performance and load test functionality was deprecated after Visual Studio 2019.
VegetaMIT LicenseLocalFreeHTTP applications
WebLOADRadView Software LtdProprietaryLocal, cloud-basedFree trial, demo, contact for pricingWeb and Mobile applications and APILoad testing tool for web and mobile applications including Web Dashboard for performance test analysis. Used for large-scale loads which can be generated also from the cloud. Licensed.
OctoPerfOctoPerfProprietaryLocal & Cloud-BasedFree plan, paid plans, contact for pricingWebsites, web applications, mobile, databases, and other scenariosSaaS and On-Premise load testing tool