Image: Rystic
Why it mattersAn agent that writes to a real system can cause real damage on its first run. A local copy of that system lets a team find the damage before a customer does.
An AI agent given write access to a real system can do real damage on its first run. One of Rystic's founders describes an earlier agent he deployed. It created hundreds of pull requests on GitHub in a few minutes. The pull requests flooded the team's CI runners.
Rystic launched out of Y Combinator Fall 2026 with local copies of 17 third-party services. The YC launch page received eight votes in its first hours. The founders are Evan Whitehouse and Zachary Kiihne. They want to let a team test what an agent does to Slack, Stripe or Google Drive. The team runs that test before pointing the agent at a real account.
What the simulators do
Rystic says each service it supports runs as a small binary. The binary keeps state. A test can delete a record and then query it. The simulator returns the same error the real service would return. Each test job gets its own isolated copy, so tests can run in parallel. The company says 50 Stripe test jobs finished in 19 seconds on its own setup. The same jobs took more than 40 minutes on shared real-API sandboxes, Rystic says.
The product covers Slack, Stripe and Google Drive by name on the launch page. The company's own site lists 14 other tools. The simulators are checked against the real services every day, Rystic says. For Stripe, the match rate is 99.1 percent of 1,813 daily checks. Every known difference is listed on the simulators page, the company says.
Testing what the agent does, not what it says
The founders write that the real test is the agent's effect on a system, not the words it produced. A simulator records every call. A test can then check what the agent actually changed in Slack or Stripe. The team no longer has to read the chat log and trust a plausible claim. The simulator can also script failure cases. The founders list two: a tripled latency and a dropped websocket connection in the middle of placing an order.
Who built it
Whitehouse graduated from Columbia Computer Science and worked on Roblox's service mesh. Kiihne spent five years at Google. He built AI features in Gmail and Google Docs, the launch page says. The pair met in 2016 playing Magic: The Gathering at the professional level.
Pricing and availability
The launch page says Rystic is free to try at rystic.ai. Custom environments, including simulators of a team's internal services, are offered through the founders by email, the launch says.
A team adopting Rystic has one real decision to make. The simulator closes the gap on 99 percent of calls to the real service. The other one percent is the gap. A test can pass on the simulator and fail on the real service. That is a bug the test will not catch. Reading the published difference list for each tool, before trusting the test, is the honest step.
Source
- Primary source: Rystic on Y Combinator.
- Product site: Rystic.
This item was written by an AI system from the linked source. Reveneau is responsible for what it publishes.
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