Migrate old React and Angular apps to modern stacks, and prove the migrated app still behaves like the original.

What is this?

You know the app: it works fine, but it's pinned to React 16, or Angular 8, or a webpack from another era. Nobody wants to touch it. Every "just upgrade it" attempt turns into a month of whack-a-mole.

versionless is a command-line tool for exactly that app. Point it at the code, and it does three things:

1. Reads the app: framework, version, builder, what era of Node it expects.
2. Rewrites it into a separate folder (a lane). It never writes into your original app. Not one byte.
3. Proves the result: installs, builds, then drives both the old app and the new one through the same journeys in a real browser, checking they behave the same.

Lots of tools can rewrite code. versionless won't call a migration done until a browser has watched the migrated app act like the original.

Install

npm install -g versionless

Requires Node 22 or newer.

Try it

# What is this app? (read-only, can't hurt anything)
versionless analyze <app-root>

# What would change? (composes the plan, writes nothing)
versionless plan <app-root>

# Do it: into a separate lane, never into the app itself
versionless migrate <app-root> --out <lane>

# Run every offline self-check in one summary
versionless verify

# What is actually supported? (generated from real runs, never hand-edited)
versionless supported-matrix

Every command takes --help and --json. Start with analyze.

The one honest rule

versionless refuses instead of guessing. If it hits something it doesn't understand (a framework it has no adapter for, a lockfile from a different package manager), it stops and tells you by name:

refused: install.lockfile-foreign

That's not a crash. Every refusal has a name, every name is counted, and some can be lifted with an explicit flag (like --allow-foreign-lockfile). You make that call, out loud, and it's recorded in the run's receipt. Nothing is silently assumed on your behalf.

What "supported" means

The support table is generated from receipts of real migrations: a real app, really migrated, really witnessed in a browser. If it's not in the matrix, it's not supported, and unknown is reported as unknown, never "probably fine." Run versionless supported-matrix to see where things stand.

Going deeper

The full evidence program (every proof, every refusal, every receipt) lives in the repository: github.com/compiled-run/versionless.

Status: active evidence program. This is evidence, not certification; the generated reports state every boundary precisely.