mops check-stable

Check stable variable compatibility between a previously deployed version and the current canister entrypoint

mops check-stable <old-file> [canister]

Verifies that an upgrade from an old actor to the current canister entrypoint is safe — i.e., that stable variable signatures are compatible. This prevents Memory-incompatible program upgrade traps at deploy time.

The command handles the full workflow internally: generating .most stable type signatures, comparing them, and cleaning up intermediate files.

Examples

Check upgrade compatibility using the old source file

mops check-stable .old/src/backend/main.mo

Check using a pre-generated .most file

mops check-stable /path/to/deployed.most

Check a specific canister in a multi-canister project

mops check-stable .old/src/backend/main.mo backend

Check with verbose output

mops check-stable .old/src/backend/main.mo --verbose

Arguments

<old-file>

Path to the old (deployed) version of the actor. Accepts two formats:

• .mo file — the old Motoko source file. The command generates the .most stable type signature automatically.
• .most file — a pre-generated stable type signature. Used directly without compilation.

[canister]

Name of the canister to check against (as defined in mops.toml). The current entrypoint is resolved from [canisters.<name>].main.

When omitted:

• If there is exactly one canister defined, it is used automatically
• If there are multiple canisters, an error is shown listing the available names

Options

--verbose

Show detailed output including the moc commands being run and the intermediate file paths.

Passing flags to the Motoko compiler

Any arguments after -- are forwarded to moc when generating stable type signatures.

mops check-stable .old/src/main.mo -- --experimental-stable-memory=1

tip

Global moc flags configured in [moc].args are automatically applied. See mops.toml reference.