SmolVM is a new CLI tool that lets developers build and run portable, lightweight virtual machines with hardware isolation. The tool creates sub-second cold starts and cross-platform compatibility for macOS and Linux, packing entire stateful environments into single .smolmachine files that rehydrate anywhere the host architecture matches.

Built on libkrun VMM with custom kernel support, SmolVM runs each workload in its own kernel using Hypervisor.framework on macOS or KVM on Linux. The default configuration provides 4 vCPUs and 8 GiB RAM with elastic memory usage via virtio balloon, meaning the host only commits what the guest actually uses. This architecture enables true isolation while maintaining near-zero overhead when over-provisioning resources.

Developers can use SmolVM for sandboxing untrusted code, creating portable executables, or setting up persistent development environments. The tool supports SSH agent forwarding without exposing private keys to the guest VM, and allows declarative environment configuration through Smolfile TOML files. Compared to alternatives like containers, Colima, QEMU, and Firecracker, SmolVM offers faster boot times under 200ms and embeddable SDK capabilities while maintaining hardware-level isolation.