Dfinity Official Mops Cli

---
name: mops-cli
description: "Manage Motoko projects with the mops CLI — toolchain pinning, dependency management, type-checking, building, and linting. Use when working with mops.toml, mops.lock, running mops commands, adding/removing packages, pinning moc or lintoko versions, checking or building canisters, configuring moc flags, or setting up a new Motoko project."
license: Apache-2.0
compatibility: "mops >= 3.1.0"
metadata:
  title: Mops CLI
  category: Infrastructure
---

# Mops CLI

Opinionated guide for Motoko projects. Covers project config, dependency management, type-checking, building, and linting.

## Key Principles

1. **No dfx** — mops neither invokes nor supports `dfx`. There is no `mops toolchain init`, no `moc-wrapper`, and no `mops watch --generate` / `--deploy`. Always pin `moc` in `[toolchain]`; every command that compiles requires it. Use the newest `moc` version. Pin `pocket-ic` too if you have replica tests, benchmarks, or `--check-deploy` — with no pin those commands error, naming `mops toolchain use pocket-ic 15.0.0`. When `MOPS_POCKET_IC_URL` points at an already-running PocketIC server, no pin is needed and an existing pin is ignored with a warning — do not add one to silence it; unset the variable instead.
2. **No `mo:base`** — it is deprecated. Always use `mo:core` (`import Array "mo:core/Array"`).
3. **All config in `mops.toml`** — canisters, moc flags, toolchain versions, build settings.
4. **Canister-centric workflow** — define all canisters in `[canisters]`; never pass file paths to `mops check`. Exception: library packages (no `[canisters]`) use file paths directly: `mops check src/**/*.mo`.

## Project Setup

### Minimal `mops.toml`

```toml
[toolchain]
moc = "1.7.0"
lintoko = "0.10.0"
pocket-ic = "15.0.0"  # required for replica tests / benchmarks / --check-deploy

[dependencies]
core = "2.5.0"

[moc]
args = ["--default-persistent-actors", "-W=M0223,M0236,M0237"]

[canisters.backend]
main = "src/backend/main.mo"

[canisters.backend.migrations]
chain = "src/backend/migrations"
check-limit = 10   # optional — speeds up `mops check` when the chain gets long

[canisters.backend.check-stable]
path = "deployed/backend.most"

[build]
outputDir = "src/backend/dist"
args = ["--release"]
check-wasm = true    # optional: analyze final Wasm complexity
check-deploy = true  # optional: verify fresh PocketIC installation after build

# Opt-in Wasm optimization (Binaryen wasm-opt) for build + bench
[optimize]
# level = "O3"       # default
# keep-names = true  # default
# wasm-opt pin: [toolchain] wasm-opt = "131" (required when [optimize] is set)
```

`check-stable` runs ICP's upgrade-time stable-variable compatibility check locally, so incompatible changes fail in `mops check` instead of being rejected when upgrading a live canister. It compares the current code against a `.most` from the deployed version.

Bootstrap that `.most`: new project → `mops deployed init` (empty-actor baseline); already-deployed canister → build from the deployed commit, then `mops deployed`. After every deploy, run `mops deployed` to promote the just-built `.most` (see [`mops deployed`](#mops-deployed) below).

Optional canister fields: `candid` (path to .did for compatibility checking), `initArg` (Candid-encoded init args).

### Warning Flags

`-W=M0223,M0236,M0237` — redundant type instantiation (M0223), suggest contextual dot notation (M0236), suggest redundant explicit arguments (M0237). These are allowed (disabled) by default; `-W=` enables them as warnings.

### Moc Args Layering

Flags are applied in this order (later overrides earlier):

1. `[moc].args` — global, all commands (check, build, test, bench, etc.)
2. `[build].args` — build only (e.g. `--release`)
3. `[canisters.<name>.migrations]` — auto-injected `--enhanced-migration` (managed by mops)
4. `[canisters.<name>].args` — per-canister
5. CLI `-- <flags>` — one-off overrides; supported by `mops check`, `mops build`, `mops check-stable`, `mops generate`, `mops migrate`, `mops test`, and `mops bench`

## Core Commands

### `mops install`

```bash
mops install            # dev flow: keeps mops.lock in sync, self-heals a broken one
mops install --locked   # CI flow: fail if mops.lock is missing or would change
```

Run after cloning or after manual `mops.toml` edits. `mops.lock` is always maintained — there is no flag to opt out, and no `--lock` flag (removed in v3). A missing, unparseable, legacy-format or `mops.toml`-inconsistent lock is regenerated by a plain `mops install`, including locks that still carry absolute local paths from older CLIs.

`--locked` requires an up-to-date lock and never writes it. It is also available on every implicitly-installing command (`mops build`, `mops check`, `mops check-stable`, `mops check-candid`, `mops test`, `mops bench`, `mops generate candid`), so CI can run `mops test --locked` with no prior install. `mops sources` has no `--locked` (a packtool caller parses its stdout mid-build) — put `mops install --locked` earlier in the pipeline instead.

The `CI` env var no longer affects lockfile behavior (removed in v3). Commit `mops.lock` — for applications and libraries alike.

A lock also goes stale when a local `path` dependency's own `mops.toml` changes — including one nested further down the chain. `mops install` regenerates it; `--locked` fails until the regenerated lock is committed. Note the first `mops install` after upgrading regenerates the lock of any project that has a `path` dependency, so commit it before running `--locked` in CI. Projects without `path` dependencies keep their existing lock.

`{MOPS_ENV}` in a `path` dependency expands to `$MOPS_ENV` (default `local`), which makes the lock environment-specific. Switching `MOPS_ENV` makes it stale: `mops install` regenerates it, and `--locked` fails with a message naming `MOPS_ENV`. Keep one lock per environment, or drop `--locked` — a lock generated under one `MOPS_ENV` will not satisfy `--locked` under another.

Integrity is verified at download time, so `mops install` no longer re-hashes `.mops/`: editing a dependency in place will not fail the next install. Use `mops verify` for the on-demand on-disk audit.

Downloaded files are always checked before anything enters the cache — against `mops.lock` when it already records the package, otherwise against the registry. A committed lock therefore makes verification free, which is why a clean checkout installs without asking the registry about hashes.

Two consequences worth knowing: a corrupt or hand-edited `mops.lock` now fails a _download_ (the error names `mops.lock` as a possible culprit — restore it from version control; already-cached packages are unaffected), and a package the registry publishes no hashes for still installs, unverified, with a warning.

Packages download in parallel through a bounded pool. `mops install --concurrency <n>` or the `MOPS_CONCURRENCY` env var (works on every installing command) caps simultaneous registry requests; the default derives from the CPU count and the file-descriptor soft limit (4–16). Transient network errors (`fetch failed`, `ECONNRESET`, `EMFILE`) retry automatically with the concurrency halved, up to twice. Set `MOPS_CONCURRENCY=1` only if installs still fail after the retries (an egress proxy capping connections, for example).

### `mops verify`

```bash
mops verify   # re-hash .mops/ against mops.lock, and mops.lock against the registry
```

Covers GitHub dependencies as well as registry ones.

Exits 1 with the offending files and a recovery hint. This is the replacement for anyone who relied on `mops install` failing when `.mops/` had been modified.

### `mops add <package>`

```bash
mops add core             # latest version
mops add core@2.5.0       # specific version
mops add --dev test       # dev dependency
mops add org/repo         # GitHub shorthand (also accepts a full github.com url)
mops add ./pkg            # local package directory
```

Updates `mops.toml` and `mops.lock`.

Adding a package that is already declared in the other section **moves** it rather than declaring it twice. `<pkg>@<version>` replaces the declared version and reports what it replaced; it leaves pinned aliases like `"core@1.0.0" = "1.0.0"` alone, and there is no flag to create one — write it by hand.

### `mops check`

Primary correctness command — runs moc check, then check-stable (if configured), then lint (if lintoko is in toolchain).

On moc 1.12.0+, canisters with `[migrations]` get stricter upgrade diagnostics: a field the initial actor requires that no migration produces fails as an `M0267` error instead of only warning (`M0254`), and compat errors carry a source location. **Temporarily disabled** — `moc --stable-baseline` is buggy, so every pin runs the pre-1.12.0 check. Older moc pins and canisters without `[migrations]` are unaffected either way.

The `check-stable` baseline is always a `.most` file — as `[canisters.<name>.check-stable].path` or as the `mops check-stable <baseline.most>` argument. A `.mo` source is rejected. See [`mops deployed`](#mops-deployed) for where the baseline comes from — that differs between a fresh project and an already-deployed canister.

```bash
mops check                # all canisters
mops check backend        # single canister
mops check --fix          # autofix + check + stable + lint
mops check --no-lint      # skip the lint step for one run
mops check --verbose      # show moc invocations
mops check -- -Werror     # treat warnings as errors
```

**Always use canister names, not file paths.** Per-canister args from `mops.toml` are applied automatically.

`--fix` applies machine-applicable fixes from both moc and lintoko in one pass. Concurrent `--fix` runs (across processes) serialize automatically via an advisory lock at `.mops/fix.lock` — safe to invoke from multiple agents on the same project. Read-only files (e.g. frozen migrations) are skipped with a warning, not fixed.

### `mops build`

```bash
mops build                # all canisters
mops build backend        # single canister
mops build --verbose      # show compiler commands
mops build --check-wasm   # analyze final Wasm complexity without PocketIC
mops build --no-check-wasm # skip configured [build].check-wasm once
mops build --check-deploy  # verify fresh installation on PocketIC
mops build --no-check-deploy # skip configured [build].check-deploy once
mops build -- --ai-errors # pass extra moc flags
```

Produces `.wasm`, `.did`, and `.most` files in `[build].outputDir` (default `.mops/.build`).

With `[optimize]` in `mops.toml`, runs `wasm-opt` after candid metadata (default `-O3 -g`). Requires a Binaryen pin: `mops toolchain use wasm-opt 131`. Build commands never write the pin themselves, and a `wasm-opt` failure fails the build. Pass `--no-optimize` (on `build` or `bench`) to skip the pass for a single run without editing `mops.toml`.

When `--check-wasm` or `[build].check-wasm = true` is enabled, Mops runs fast Walrus analysis on the final Wasm without starting PocketIC. Per-function IC0505 complexity below 750,000 is quiet, 750,000 through 899,999 emits an early warning, and 900,000 or more emits a critical warning. `MOPS-WASM-COMPLEXITY` output includes actionable function metrics, the three largest complexity contributors, and Motoko correction guidance. The estimate never fails the build. Use `--no-check-wasm` to skip configured analysis once.

### `mops deployed`

Post-deploy hook — keeps the on-disk `.most` baseline used by `check-stable` in sync with what's actually deployed.

```bash
mops deployed init backend   # one-time bootstrap: empty-actor baseline + sets [check-stable].path
mops deployed backend        # post-deploy: promotes .mops/.build/backend.most → deployed/backend.most
mops deployed                # all canisters
```

Default destination is `deployed/<name>.most`; override with `[deployed].dir` in `mops.toml` or `--dir`. It reads built `.most` files from `[build].outputDir` (default `.mops/.build`); override with `--build-dir`. `mops deployed` errors if the source `.most` is missing — it never regenerates. Run it from your deploy pipeline immediately after a successful deploy.

### `mops generate candid`

```bash
mops generate candid                # all canisters
mops generate candid backend        # single canister
mops generate candid backend -o <path>   # single canister, ad-hoc path
```

(Re)generates the curated `.did` from current Motoko source. With `[canisters.<name>].candid` set, overwrites that file. Without it, writes `<name>.did` next to `main` (e.g. `main = "src/Backend.mo"` → `src/backend.did`) and sets `[canisters.<name>].candid` in `mops.toml`. Run after every interface change; commit `.did` + `mops.toml` together. Same moc invocation as `mops build`, so the result always passes `mops build`'s subtype check.

### `mops toolchain`

```bash
mops toolchain use moc 1.7.0         # pin specific version
mops toolchain use moc latest        # pin latest version (non-interactive)
mops toolchain use lintoko 0.10.0    # pin specific version
mops toolchain use pocket-ic 15.0.0  # pin for replica tests / benchmarks / --check-deploy
mops toolchain use wasm-opt 131      # Binaryen for [optimize] (or `latest`)
mops toolchain update moc            # update to latest (requires existing [toolchain] entry)
mops toolchain update                # update all tools to latest
mops toolchain info <tool>           # show release info (latest, pinned, history)
mops toolchain info <tool> --versions # list recent stable releases, newest first
mops toolchain info <tool> --versions --all # full stable history (cache warming)
mops toolchain bin moc               # print path to binary
```

**`pocket-ic` versions**: pin anything from `9.0.0` up, `latest` included — mops keeps no list of blessed versions. Pins below `9.0.0` error with a migration message (they ran on the legacy client that mops 3.0.0 removed). With no pin, replica tests / `mops bench` / `--check-deploy` / `mops toolchain bin pocket-ic` error naming `mops toolchain use pocket-ic 15.0.0`. That version is a hint, not a fallback.

**Agent note**: `toolchain use <tool>` without a version opens an interactive picker — do not use in scripts or agents. Always pass a version or `latest`. `toolchain update` only works when the tool already has a `[toolchain]` entry. `toolchain info <tool> --versions` works without `mops.toml` (first GitHub page by default; pass `--all` for full history).

### Enhanced migrations

When `[canisters.<name>.migrations]` is configured, `mops check`, `mops build`, and `mops check-stable` automatically inject `--enhanced-migration`. Do not add `--enhanced-migration` to `[canisters.<name>].args` — mops will error.

Create migration files directly in the `chain` directory.

After `mops check --fix` (or `mops check <canister>`) confirms the chain compiles, run `mops build` to produce the wasm artifact.

Use `mops build --check-deploy`, or set `[build].check-deploy = true` for every build, to install each built Wasm on a fresh PocketIC canister and catch module validation, initialization, and installation failures. Requires `[toolchain] pocket-ic` (a version from `9.0.0` up, or a local binary path) — or set `MOPS_POCKET_IC_URL` to an already-running PocketIC server (the pin is then ignored). Unpinned with no URL, the build errors naming `mops toolchain use pocket-ic 15.0.0`. Use `--no-check-deploy` to skip configured validation once. The command uses each canister's `initArg`, or `()` when omitted. Set `wasmMemoryLimit` to a positive integer byte limit on a canister to check deployment under that limit. PocketIC errors are reported as provided by the client, and installation failures are collected across canisters. Before installation, Mops runs `moc --stable-compatible` from a temporary empty-actor `.most` to each generated `.most`. If moc reports incompatibility, Mops emits `MOPS-CHECK-DEPLOY-SKIPPED` with the compiler diagnostic and does not check that canister on fresh PocketIC. Eligible siblings are still checked; validate the skipped upgrade against representative baseline state.

`check-limit` (optional) caps how many recent chain files `mops check` and `mops lint` consider — useful when the chain grows long and re-checking every old migration slows feedback down. `mops build` is unaffected by `check-limit`. When the limit kicks in, mops stages the included files into `.migrations-<canister>/` next to the `chain` directory (auto-`.gitignore`d). `moc` diagnostics may then print paths there — the real file lives in the `chain` directory with the same name.

Override `check-limit` for a single run with `--no-check-limit` (`mops check`, `mops check-stable`, `mops lint`) — e.g. `mops check --fix --no-check-limit` to autofix older, normally-trimmed migrations. On `mops check` and `mops check-stable`, `--no-check-limit` also suppresses the pending-migration warning.

When `check-limit` is set, `mops check-stable` (and the stable check inside `mops check`) reports if more migrations are pending than the limit allows — as an error if compat failed (replacing the misleading `moc` message), otherwise a warning.

### `mops remove <package>`

```bash
mops remove core
```

Removes from whichever section declares the package; `--dev` limits it to `[dev-dependencies]`. A package declared in both sections is removed from both.

### Dependency Management

```bash
mops outdated             # list outdated deps (caret-bound); exit 1 if any, 2 if the check failed
mops outdated core        # check a single package
mops update               # rewrite mops.toml versions within caret bound (no major-version crossing)
mops update core          # update specific package within caret bound
mops update --major       # allow updates that cross major versions
mops update --patch       # restrict to patch bumps only (mutually exclusive with --major)
mops update --verbose     # verbose output
mops sync                 # add missing / remove unused packages
mops sync --dry-run       # print what would change, write nothing
```

`mops update` rewrites `mops.toml` in place (like `cargo upgrade`, not `cargo update`) and re-pins GitHub dependencies to their branch head. Like `mops outdated`, it exits `2` when it cannot run or complete — no `mops.toml`, a package that is not declared, or a dependency that failed to update (the other dependencies are still updated).

`mops sync` needs a pinned `[toolchain] moc` — it reads imports with `moc --print-deps`. Packages imported only from `test`/`tests`/`bench`/`benchmark` directories are added to `[dev-dependencies]`; already-declared packages are never moved between sections.

## Other Commands

### `mops publish`

```bash
mops publish              # publish to the registry (runs tests/docs/bench by default)
mops publish --dry-run    # same local steps as publish; no registry contact / identity
mops publish --dry-run --no-test --no-docs --no-bench   # packaging checks only
mops publish --no-test --no-docs --no-bench
```

`--dry-run` runs the same local publish pipeline (packaging checks, docs, changelog, tests, benchmarks) and prints the final file list, then stops before identity/upload. `--no-*` flags work as usual. It does **not** run canister config validation (SPDX/semver/name rules) or prove registry acceptance (already published, permissions, missing deps).

### `mops test`

Tests live in `test/*.test.mo`:

```bash
mops test                         # run all tests
mops test my-test                 # filter by name
mops test --mode wasi             # use wasmtime (for to_candid/from_candid)
mops test --reporter files        # one line per file (default is verbose)
mops test --watch                 # re-run on file changes
mops test -- -Werror              # pass extra moc flags
```

Replica tests (actor files or `// @testmode replica`) run on PocketIC — the `pocket-ic` version from `[toolchain]`, or an already-running server when `MOPS_POCKET_IC_URL` is set (no pin needed; canister log output is not streamed in attached mode). Unpinned with no URL, they error naming `mops toolchain use pocket-ic 15.0.0`. Same for `mops bench` and `mops watch --test`. There is no `--replica` flag and no dfx replica.

### `mops bench`

Benchmarks live in `bench/*.bench.mo`:

```bash
mops bench                        # run all benchmarks
mops bench my-bench               # filter by name
mops bench --gc incremental       # select GC
mops bench --save                 # save results to .bench/<name>.json
mops bench --compare              # compare with saved results
mops bench -- -Werror             # pass extra moc flags
```

### `mops lint`

Runs lintoko (also runs automatically as part of `mops check` when lintoko is in toolchain):

```bash
mops lint                 # lint all .mo files
mops lint --fix           # autofix lint issues
mops lint <name>          # filter to .mo files matching <name>
```

When `[canisters.<name>.migrations].check-limit` is set, `mops lint` skips the trimmed chain migrations to match what `moc` sees during `mops check`. To lint a trimmed migration on demand, pass an explicit filter (e.g. `mops lint OldMigrationName`) or `--no-check-limit` to lint the full chain.

### `mops format`

```bash
mops format               # format all .mo files
mops format --check       # check formatting without modifying
```

### `mops watch`

```bash
mops watch                # errors + warnings + format (the default set)
mops watch --warning      # errors + warnings only
mops watch -t             # errors + tests
```

Error checking is always on. Passing any flag selects only the named tasks, so add `-w` / `-f` when you want them alongside `-t`. Those four are the whole set — there is no `--generate` or `--deploy`.

## Common Patterns

### Warning suppression for a canister

Use per-canister `args` (not global) for suppressions:

```toml
[canisters.backend]
main = "src/backend/main.mo"
args = ["-A=M0198"]
```

### New project

```bash
mops init -y
mops toolchain use moc latest        # pin latest moc (non-interactive)
mops toolchain use lintoko latest    # pin latest lintoko
mops add core
```

Then configure `[moc].args`, `[canisters]`, and `[build]` in `mops.toml`.

To update tools later: `mops toolchain update moc` or `mops toolchain update` (all tools).