LocalStack has acquired WonderTwin AI, adding local application emulators for software integration testing to its development platform.
WonderTwin AI builds local emulators for third-party applications including GitHub, HubSpot, PostHog and Stripe. LocalStack plans to integrate those tools into its platform so developers and AI agents can test software connections locally rather than against live application programming interfaces.
The acquisition brings together two areas of software testing that are becoming more important as engineering teams adopt more automated coding tools. LocalStack simulates cloud environments such as AWS and Snowflake on local infrastructure, while WonderTwin AI reproduces the behaviour of external software services that applications rely on.
Together, they address a common software development problem. Teams building integrations with outside services often have to test code in shared sandbox environments or against live systems, creating delays, raising security concerns and increasing costs.
In AI-assisted development, those constraints can be even more acute because multiple developers and software agents may need to run tests at the same time. Local emulation lets each user or agent work in a separate environment without access to third-party systems.
Waldemar Hummer, co-founder and chief technology officer of LocalStack, said users had been pushing beyond cloud-only development tools.
"As the way engineers build software continues to evolve, our community is discovering gaps in the stack supporting those workflows," Hummer said. "Cloud applications rarely operate in isolation. With WonderTwin AI, we're extending local development beyond cloud infrastructure to include the third-party APIs and external services applications depend on."
Testing pressure
The issue is especially relevant for teams building and maintaining integrations with software-as-a-service applications. Traditional testing methods often depend on shared environments provided by outside vendors, which may not handle large volumes of concurrent testing activity well.
That can slow release cycles and make it harder to validate changes before software reaches production. For companies using AI agents in development workflows, it can also limit how much work those systems can do without human involvement.
Local emulators can help reduce those bottlenecks by letting developers test code updates immediately, inspect failures earlier and avoid waiting for access to remote sandboxes. They can also allow AI agents to validate integrations and cloud behaviour without direct access to third-party applications.
Tela Andrews, founder of WonderTwin AI, said existing SaaS testing setups had become inadequate for AI-driven workflows.
"The SaaS application testing environment has always been limited. AI agents broke it completely," Andrews said. "Emulation was the only fix. Joining LocalStack brings full-stack emulation for applications and cloud platforms together under one roof to make concurrent, local validation seamless for any developer and any agent."
Broader platform
LocalStack has built its business around helping developers reproduce parts of cloud environments on their own machines or in isolated infrastructure. By adding WonderTwin AI's application emulators, it is broadening that model from cloud services to the wider set of external tools used in modern software stacks.
The target users are engineering organisations that need to validate both infrastructure behaviour and application integrations before release. Instead of connecting test code to live third-party services intended for production workloads, teams would be able to run isolated local copies of those dependencies.
That could also affect continuous integration and continuous delivery pipelines, where repeated tests can be slowed by network delays, access restrictions and usage costs tied to real services. Running those checks locally may allow teams to execute tests more quickly without consuming live resources.
LocalStack has more than 1,500 customers and has recorded hundreds of millions of Docker pulls. It has become a widely used tool for local cloud development, particularly among teams that want to mirror cloud setups without relying on remote accounts at every stage of testing.
WonderTwin AI's technology is expected to extend that approach to a growing list of software applications used in business workflows, including developer tools, customer software and payment systems. Initial examples include GitHub and PostHog, with other application emulators also part of the offering.
The acquisition reflects a wider shift in software engineering towards isolated development environments that can support both human programmers and automated agents at the same time.