Configuration

Environment variables

Variable	Effect
RIGHTSIZE_BACKEND	Force microsandbox or docker, overriding auto-selection.
MSB_PATH	Use a pre-installed msb binary; skips the download/provisioning step entirely.
RIGHTSIZE_CACHE_DIR	Relocate the runtime cache (default ~/.cache/rightsize).
RIGHTSIZE_MSB_SKIP_DOWNLOAD	true = fail with guidance instead of downloading — for air-gapped CI; pair with MSB_PATH or a pre-seeded cache.
RIGHTSIZE_REAPER	on (default) / sweep / off — controls orphan reaping. See Orphan reaping.
RIGHTSIZE_REUSE	true or 1 — the second half of reuse's double opt-in (paired with .withReuse() on the builder). See Container reuse.
DOCKER_HOST	A unix:// socket path (or bare path) for the Docker backend to dial instead of the default /var/run/docker.sock.

See Backends for how these combine with automatic selection.

Runtime support

Runtime	Minimum
Node.js	>=22.11 (the 22.x "Jod" LTS line)
Bun	>=1.1

The library is authored in TypeScript using await using, and compiled to ES2022 plus the downlevelled explicit-resource-management helpers — the shipped dist/**.js runs unmodified on both runtimes with no flags. Node 22.11+ carries the Symbol.asyncDispose global those helpers dispatch to; Bun ships it natively. See the Lifecycle guide for what this buys you.

Development

npm install                 # installs dependencies
npm run build                # compiles src/ to dist/
npm run typecheck            # tsc --noEmit
npm test                     # unit suite, both runtimes (test:node + test:bun)
npm run coverage:core        # core coverage, 80% line floor

Integration tests boot real containers and are gated behind RIGHTSIZE_IT=1, forcing a backend explicitly:

RIGHTSIZE_BACKEND=microsandbox npm run test:node:it   # needs Apple Silicon or Linux + /dev/kvm
RIGHTSIZE_BACKEND=docker npm run test:node:it         # needs a reachable Docker daemon

Docs:

npm run docs:dev             # local dev server
npm run docs:build           # static build
npm run docs:verify          # extracts every fenced ts/typescript block from
                              # README.md + docs/** and typechecks it
npm run docs:api-check       # fails on any undocumented public API surface