WebAssembly (Wasm) VMs are increasingly used on microcontroller units (MCUs), enabling multiple programming languages to run on resource-constrained devices. However, debugging and testing MCU applications remains challenging, particularly due to concurrency bugs caused by interrupts and message interleavings. Existing tools are often limited to native C/C++ programs, operate only at the bytecode level, or are too slow for practical debugging or testing.

In this demo, we present Wasmito, a framework for building lightweight dynamic tools for Wasm applications running on the WARDuino MCU VM. Wasmito allows developers to register callbacks for runtime events such as function calls, interrupts, and memory accesses, while executing analysis logic on a desktop machine. We demonstrate Wasmito with two tools: a record-and-replay debugger and an automated detector for interrupt-related concurrency bugs.