API Latency Simulator

See how your app handles slow APIs

Applications behave differently when the APIs they call are slow, and testing only against fast local responses hides problems. This tool simulates API response delays, so you can test how your application behaves under latency before real users hit it.

Why testing under latency matters

In development, APIs respond instantly, so loading states, timeouts and race conditions never trigger, and the code that handles them goes untested. In production, real networks are slow and variable, and that untested code fails, a spinner that never appears, a timeout set too short, a race between two slow calls. Simulating latency surfaces these issues while you can still fix them cheaply. It is the kind of testing that separates an application that feels robust on a poor connection from one that falls apart, which is most users’ real experience.

Robust under real conditions

It runs entirely in your browser, so nothing you paste is uploaded and the result is yours to copy straight into a project. Because it works client-side, you can use it on private code and data without anything leaving your machine.

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