diff --git a/AGENTS.md b/AGENTS.md
index b5fcab9..7298af6 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -6,84 +6,86 @@ Wasm file (with embedded WIT custom section) and generates Go bindings targeting
 
 ## Build & Run
 
+Every routine operation is a `just` recipe; `just --list` shows them all.
+
 ### Prerequisites
 
-- Rust toolchain (version pinned to what's in in `rust-toolchain.toml`)
-- `wasm32-unknown-unknown` and `wasm32-wasip1` targets (configured in
-  `rust-toolchain.toml`)
+- [just](https://just.systems/)
+- Rust toolchain (version pinned in `rust-toolchain.toml`).
+  `just install` installs it with the `wasm32-unknown-unknown` and
+  `wasm32-wasip1` targets the file configures.
 - Go (for running example tests)
 
+The recipes ignore an inherited `RUSTUP_TOOLCHAIN` or `CARGO_TARGET_DIR`, so
+they use the toolchain pinned in `rust-toolchain.toml` and the `target/`
+directory that `examples/generate.go` reads from.
+
 ### Building
 
 ```sh
-cargo build
+just build
 ```
 
 ### Running
 
 Gravity takes a Core Wasm file and produces Go source + an optimized `.wasm`
-file:
+file. `just run` passes its arguments to gravity:
 
 ```sh
-cargo run --bin gravity -- --world <world-name> --output <output.go> <input.wasm>
+just run --world <world-name> --output <output.go> <input.wasm>
 ```
 
 ## Testing
 
+`just check` runs the same steps as `.github/workflows/ci.yml`, in the same
+order: format check, build, unit tests, the Go example tests and the CLI
+snapshot tests. Each step is also its own recipe, described below.
+
 ### Unit Tests
 
 Run all unit tests (does NOT include snapshot/CLI tests):
 
 ```sh
-cargo test
+just test
 ```
 
 ### Snapshot / CLI Tests
 
-The CLI tests use `trycmd` for snapshot testing and require the example Wasm
-files to be built first. They are excluded from the default `cargo test` run.
+The CLI tests use `trycmd` for snapshot testing and read the example Wasm
+files, so `just test-cli` builds every example first. They are excluded from
+`just test`.
 
 ```sh
-# 1. Build example Wasm files
-cargo build -p example-basic --target wasm32-unknown-unknown --release
-cargo build -p example-iface-method-returns-string --target wasm32-unknown-unknown --release
-cargo build -p example-instructions --target wasm32-unknown-unknown --release
-cargo build -p example-regressions --target wasm32-unknown-unknown --release
-
-# 2. Run CLI snapshot tests
-cargo test --test cli
+just test-cli
 ```
 
-To update snapshot expectations when output changes intentionally:
+To update snapshot expectations when output changes intentionally, then read
+the diff before committing it:
 
 ```sh
-TRYCMD=overwrite cargo test --test cli
+just update-snapshots
 ```
 
 Snapshot files live in `cmd/gravity/tests/cmd/` (`.toml` for config, `.stdout`
 and `.stderr` for expected output).
 
 **Important**: The `trycmd` dependency has the `filesystem` feature disabled.
-This means `TRYCMD=overwrite` can only update _existing_ `.stdout`/`.stderr`
-files — it cannot create new ones. When adding a new snapshot test, you must
-manually create the `.stdout` and `.stderr` files first (e.g. by redirecting
-gravity's output), then `TRYCMD=overwrite` can keep them in sync afterward.
+This means `just update-snapshots` can only update _existing_
+`.stdout`/`.stderr` files — it cannot create new ones. `just new-snapshot
+<name>` creates all three files for a new example from gravity's current
+output; after that, `just update-snapshots` keeps them in sync.
 
 ### Example Go Tests
 
 The examples include Go test files that verify the generated bindings work
-end-to-end with wazero. After building the example Wasm files and running
-Gravity to regenerate bindings:
+end-to-end with wazero. `examples/generate.go` has `//go:generate` directives
+that build each example's Wasm and run Gravity on it. `just generate` runs
+them, and `just test-go` runs them and then the Go tests:
 
 ```sh
-cd examples
-go generate ./...
-go test ./...
+just test-go
 ```
 
-Or use `go generate` from the repo root (the `examples/generate.go` file has
-`//go:generate` directives that build Wasm and run Gravity).
-
 ## Project Structure
 
 ```text
@@ -120,13 +122,18 @@ examples/
   iface-method-returns-string/  # Interface method returning a string
   instructions/          # Tests various canonical ABI instructions
   regressions/           # Regression tests for import codegen edge cases
+
+justfile                 # Recipes for building, testing and the CI gate
 ```
 
 **Note on generated files**: `examples/.gitignore` ignores all `*/*.go` files
 (except `*/*_test.go`) and all `*/*.wasm` files. This means the generated Go
 bindings and Wasm binaries are not committed — only the test files, WIT
-definitions, and Rust source are tracked. You must run `go generate ./...` from
-the `examples/` directory before the Go tests will compile.
+definitions, and Rust source are tracked. The Go tests compile only after
+`just generate` has run, which `just test-go` does first. After switching to a
+branch without an example, its directory holds only these generated files, and
+the `examples/*` workspace glob then fails every cargo command with "failed to
+load manifest"; `just clean-examples` removes them.
 
 ## Architecture
 
@@ -200,12 +207,12 @@ Bump every example's pins with them.
 ## Style & Conventions
 
 - Use conventional commits: `feat:`, `fix:`, `docs:`, `test:`, `refactor:`, etc.
-- Format code before committing with `cargo fmt`
-- Lint with `cargo clippy`
+- Format code before committing with `just format`
+- Lint with `just clippy` (CI does not run clippy)
 - When adding new instruction handlers in `func.rs`, add corresponding entries
   in the `instructions` example and update snapshot tests
-- When changing codegen output, update snapshot `.stdout` files (or use
-  `TRYCMD=overwrite`)
+- When changing codegen output, update snapshot `.stdout` files with
+  `just update-snapshots`
 
 ## Adding a New Example
 
@@ -216,9 +223,11 @@ Bump every example's pins with them.
 3. Add `//go:generate` directives to `examples/generate.go` (one for
    `cargo build`, one for `cargo run --bin gravity`)
 4. Write `examples/<name>/<name>_test.go` (this file IS committed)
-5. Create snapshot test files in `cmd/gravity/tests/cmd/`:
+5. Create the snapshot test files with `just new-snapshot <name>`, or
+   `just new-snapshot <name> <world>` when the world is not named for the
+   example. It builds the example and writes three files to
+   `cmd/gravity/tests/cmd/`:
    - `<name>.toml` — trycmd config (`bin.name = "gravity"`, `args = "..."`)
-   - `<name>.stdout` — capture with
-     `cargo run --bin gravity -- --world <name> <wasm-path> > <stdout-path>`
-   - `<name>.stderr` — typically empty (`touch <stderr-path>`)
-6. Verify: `cargo test && cargo test --test cli && (cd examples && go generate ./... && go test ./...)`
+   - `<name>.stdout` — gravity's output for the example
+   - `<name>.stderr` — empty
+6. Verify: `just check`
diff --git a/justfile b/justfile
new file mode 100644
index 0000000..7fd2465
--- /dev/null
+++ b/justfile
@@ -0,0 +1,158 @@
+# Gravity command runner.
+# Run `just --list` to see available recipes, or `just <recipe>` to run one.
+#
+# `just check` runs the same steps as .github/workflows/ci.yml, in the same
+# order. Change both together.
+
+# show available recipes (default when no recipe is given)
+[private]
+default:
+    @just --list
+
+# rust-toolchain.toml pins the toolchain CI uses; an inherited override would
+# replace it.
+unexport RUSTUP_TOOLCHAIN
+
+# examples/generate.go builds into and reads from ../target, so a relocated
+# target directory makes `go generate` fail with "unable to read file".
+unexport CARGO_TARGET_DIR
+
+# styled header: bold cyan ✦, bold white label
+h := BOLD + CYAN + "✦" + WHITE + " "
+n := NORMAL
+
+# ─── Root commands ───────────────────────────────────────────────────────────────
+
+# run the full CI gate: format check, build, unit tests, Go example tests, CLI
+# snapshot tests
+[doc('run the full CI gate')]
+[group('ci')]
+check: lint build test test-go test-cli
+
+# install the toolchain, components and targets pinned in rust-toolchain.toml
+[group('setup')]
+install:
+    @echo '{{ h }}install: rustup toolchain{{ n }}'
+    @rustup toolchain install --no-self-update
+
+# auto-format Rust code and this justfile
+[group('format')]
+format:
+    @echo '{{ h }}format: cargo fmt{{ n }}'
+    @cargo fmt --all
+    @echo '{{ h }}format: justfile{{ n }}'
+    @just --fmt
+
+# check formatting of Rust code and this justfile
+[group('ci')]
+[group('lint')]
+lint:
+    @echo '{{ h }}lint: cargo fmt{{ n }}'
+    @cargo fmt --all --check
+    @echo '{{ h }}lint: justfile{{ n }}'
+    @just --fmt --check
+
+# lint with clippy. Not part of `check`, because CI does not run clippy.
+[doc('lint with clippy (not part of the CI gate)')]
+[group('lint')]
+clippy:
+    @echo '{{ h }}lint: cargo clippy{{ n }}'
+    @cargo clippy --workspace --all-targets --locked
+
+# ─── Build and test ──────────────────────────────────────────────────────────────
+
+# build the workspace
+[group('build')]
+[group('ci')]
+build:
+    @echo '{{ h }}build: cargo build{{ n }}'
+    @cargo build --locked
+
+# run the Rust unit tests. The CLI snapshot tests are excluded; see `test-cli`.
+[doc('run the Rust unit tests')]
+[group('ci')]
+[group('test')]
+test:
+    @echo '{{ h }}test: cargo test{{ n }}'
+    @cargo test --locked
+
+# run gravity with the given arguments, e.g.
+# `just run --world basic --output basic.go basic.wasm`
+[doc('run gravity with the given arguments')]
+[group('build')]
+[positional-arguments]
+run *args:
+    @cargo run --quiet --locked --bin gravity -- "$@"
+
+# build the example wasm and generate their Go bindings
+[group('build')]
+generate:
+    @echo '{{ h }}generate: example wasm and Go bindings{{ n }}'
+    @go generate ./...
+
+# run the Go example tests against freshly generated bindings
+[group('ci')]
+[group('test')]
+test-go: generate
+    @echo '{{ h }}test: go test{{ n }}'
+    @go test ./...
+
+# run the trycmd CLI snapshot tests. They read the example wasm that
+# `generate` builds.
+[doc('run the trycmd CLI snapshot tests')]
+[group('ci')]
+[group('test')]
+test-cli: generate
+    @echo '{{ h }}test: cargo test --test cli{{ n }}'
+    @cargo test --locked --test cli
+
+# rewrite the CLI snapshot .stdout and .stderr files from current output. Read
+# the diff before committing it. trycmd cannot create a snapshot file, so a new
+# test's files must exist first; see AGENTS.md.
+[doc('rewrite existing CLI snapshot files from current output')]
+[group('test')]
+update-snapshots: generate
+    @echo '{{ h }}test: cargo test --test cli (overwrite){{ n }}'
+    @TRYCMD=overwrite cargo test --locked --test cli
+
+# create the CLI snapshot files for the example in examples/<name>: a .toml
+# that runs gravity on the example's wasm, the .stdout gravity prints for it,
+# and an empty .stderr. trycmd cannot create these files, only update them.
+# `world` defaults to the example's name. Existing files are left alone.
+[doc('create the CLI snapshot files for a new example')]
+[group('test')]
+[script('bash')]
+new-snapshot name world=name:
+    set -euo pipefail
+    name={{ quote(name) }}
+    world={{ quote(world) }}
+    base="cmd/gravity/tests/cmd/$name"
+    for ext in toml stdout stderr; do
+      if [[ -e "$base.$ext" ]]; then
+        echo "{{ style("error") }}error:{{ n }} $base.$ext already exists" >&2
+        exit 1
+      fi
+    done
+    wasm="target/wasm32-unknown-unknown/release/example_${name//-/_}.wasm"
+    echo "{{ h }}build: example-$name (wasm){{ n }}"
+    cargo build --locked -p "example-$name" --target wasm32-unknown-unknown --release
+    echo "{{ h }}snapshot: $name{{ n }}"
+    # Capture first, so a failing gravity run leaves no partial snapshot behind.
+    stdout="$(mktemp)"
+    trap 'rm -f "$stdout"' EXIT
+    cargo run --quiet --locked --bin gravity -- --world "$world" "$wasm" > "$stdout"
+    # trycmd runs gravity from cmd/gravity, so the .toml's path is relative to it.
+    printf 'bin.name = "gravity"\nargs = "--world %s ../../%s"\n' "$world" "$wasm" > "$base.toml"
+    cp "$stdout" "$base.stdout"
+    : > "$base.stderr"
+
+# ─── Cleanup ─────────────────────────────────────────────────────────────────────
+
+# remove gitignored example output. After switching to a branch without an
+# example, its directory holds only generated files, and the examples/*
+# workspace glob then fails every cargo command with "failed to load manifest".
+[doc('remove gitignored example output (generated Go and wasm)')]
+[group('setup')]
+clean-examples:
+    @echo '{{ h }}clean: examples{{ n }}'
+    @git clean -f -X -- examples/