Rystic
Rystic is a YC Fall 2026 (F26) company. Based in San Francisco, CA, USA. Team of 2.
About Rystic
Summary
Rystic builds stateful, local API simulators that let developers test and train AI agents against realistic stand-ins for services like Slack, GitHub, Stripe, and Kalshi without hitting live endpoints. Each simulator tracks state across calls and is continuously verified against the real API, so agent behavior tested locally matches production. It replaces ad-hoc mocking, sandbox rate limits, and the risk of running agents against live third-party services during development and CI.
Business model
Free tier for pre-built simulators, paid Pro plan to load custom records, and an Enterprise tier that runs fully offline.
Go-to-market
Developer teams building AI agents adopt it self-serve via a CLI installer, with free simulators serving as the entry point.
From the Y Combinator listing
API simulators for testing and training agents locally
Facts
- B2B / B2B -> Engineering, Product and Design
- San Francisco, CA, USA
- 2
- Active
- Early
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