diff --git a/README.md b/README.md
index c2a5a1b..cf9275c 100644
--- a/README.md
+++ b/README.md
@@ -38,6 +38,30 @@ cargo build --release
 The `.sqlite` is not committed. It is derived, it is 30MB, and MegaMek's data
 is CC BY-NC-SA 4.0 — build it locally.
 
+## Hooks
+
+```
+prek install
+```
+
+Installs the pre-commit and commit-msg hooks from `prek.toml`. Same set as the
+sibling repos where the file types overlap — whitespace, TOML and XML checks,
+shellcheck, `cargo fmt` and `cargo clippy` — plus two this repo needs of its
+own.
+
+`crate-boundaries` runs `scripts/check-boundaries.sh` when a `Cargo.toml`
+changes. That is the file a boundary breaks in, and the breakage otherwise
+surfaces much later as "why can this not compile to wasm".
+
+`commit-scope` checks the subject is Conventional Commits and that its scope
+names an epic in headquarters' `plan/` — `unit-library`, `unit-search`,
+`unit-rules` — or one of a short list of non-epic scopes. A commit with no
+scope passes.
+
+`cargo clippy` runs with `-j 2` here where the sibling repos do not bother: a
+full-parallel cargo build has taken this machine down, and a hook runs on
+every commit.
+
 ## What comes from where
 
 `helm-unitfile` reads MegaMek's two formats directly: `.mtf` for Meks, `.blk`
diff --git a/prek.toml b/prek.toml
new file mode 100644
index 0000000..ce18c57
--- /dev/null
+++ b/prek.toml
@@ -0,0 +1,84 @@
+# Hooks for prek (https://prek.j178.dev/). See README for setup.
+#
+# Same shape as the sibling repos, minus what this one has no files for:
+# no terraform (infra's), no prettier or astro (headquarters' web), no ruff
+# (arena's Python helpers, and there is no Python here).
+
+# The commit-msg hook needs its own git shim, so `prek install` alone does not
+# get it. Naming it here means a plain `prek install` installs both.
+default_install_hook_types = ["pre-commit", "commit-msg"]
+
+[[repos]]
+repo = "https://github.com/pre-commit/pre-commit-hooks"
+rev = "v6.0.0"
+# check-xml earns its place on one file, bridge/log4j2-quiet.xml, which
+# nothing else parses until MegaMek refuses to start. check-yaml and
+# check-json are here for the CI config this repo does not have yet; they cost
+# nothing while they match nothing.
+#
+# check-added-large-files matters more here than in the sibling repos: the
+# built database is 100MB and the bridge's dumps are 33MB, and while
+# .gitignore covers them by name, a differently-named copy would sail in.
+hooks = [
+  { id = "check-merge-conflict" },
+  { id = "check-added-large-files" },
+  { id = "check-toml" },
+  { id = "check-yaml" },
+  { id = "check-json" },
+  { id = "check-xml" },
+  { id = "mixed-line-ending", args = ["--fix=lf"] },
+  { id = "end-of-file-fixer" },
+  { id = "trailing-whitespace" },
+]
+
+[[repos]]
+repo = "https://github.com/shellcheck-py/shellcheck-py"
+rev = "v0.11.0.1"
+# Same flags as arena's and headquarters' gates: -x follows sourced files, and
+# info-level notes do not gate.
+hooks = [{ id = "shellcheck", args = ["-x", "--severity=warning"] }]
+
+[[repos]]
+repo = "local"
+
+[[repos.hooks]]
+id = "cargo-fmt"
+name = "cargo fmt"
+language = "system"
+entry = "cargo fmt --all --check"
+pass_filenames = false
+files = '\.rs$'
+
+# -j 2, which the sibling repos do not need. A full-parallel cargo build has
+# taken this machine down before, and a hook runs on every commit, so it is
+# the last place to let one off the leash.
+[[repos.hooks]]
+id = "cargo-clippy"
+name = "cargo clippy"
+language = "system"
+entry = "cargo clippy -j 2 --workspace --all-targets -- -D warnings"
+pass_filenames = false
+files = '(\.rs|Cargo\.(toml|lock))$'
+
+# The crate graph this repo's design rests on: no I/O dependency may reach the
+# crates that have to compile to wasm, and no producer of ComputedStats may
+# reach helm-db. Both erode by adding one line to a Cargo.toml, and the
+# failure surfaces much later as "why can this not compile to wasm", so the
+# trigger is Cargo.toml rather than every Rust file - a `use` cannot add a
+# dependency, and this way the hook stays off the common path.
+[[repos.hooks]]
+id = "crate-boundaries"
+name = "crate boundaries"
+language = "system"
+entry = "scripts/check-boundaries.sh"
+pass_filenames = false
+files = 'Cargo\.toml$'
+
+# Conventional Commits, with the scope naming the epic in headquarters' plan/
+# that the work belongs to. The script says what else is allowed and why.
+[[repos.hooks]]
+id = "commit-scope"
+name = "commit scope"
+language = "system"
+entry = "scripts/check-commit-scope.sh"
+stages = ["commit-msg"]
diff --git a/scripts/check-commit-scope.sh b/scripts/check-commit-scope.sh
new file mode 100755
index 0000000..afc0e03
--- /dev/null
+++ b/scripts/check-commit-scope.sh
@@ -0,0 +1,112 @@
+#!/usr/bin/env bash
+#
+# Check a commit message against Conventional Commits, and its scope against
+# the epics this repo's work belongs to.
+#
+# Two differences from headquarters' hook of the same name, both deliberate.
+#
+# It enforces the *form* as well as the scope. headquarters lets an
+# unconventional subject through, because that repo has years of them; this
+# one has had the convention from its second commit and there is no reason to
+# let it slip.
+#
+# And the epic ids are written down here rather than read from plan/, because
+# helm has no plan/ - its epics live in headquarters, which is not guaranteed
+# to be checked out beside this repo and is certainly not guaranteed to be at
+# any particular revision. A hardcoded list that is occasionally stale is
+# better than a hook that passes silently whenever a sibling directory is
+# missing.
+#
+# Run by prek at the commit-msg stage, with the message file as $1.
+
+set -euo pipefail
+
+# Conventional Commits types.
+TYPES="feat fix docs style refactor perf test build ci chore revert"
+
+# Epic ids from headquarters' plan/. Add one here when an epic that helm does
+# work for is added there.
+EPIC_SCOPES="unit-library unit-search unit-rules"
+
+# Scopes that are deliberately not epics. Keep this short: every entry is a
+# commit that cannot be found from an epic.
+NON_EPIC_SCOPES="deps scripts bridge ci repo"
+
+msg_file="${1:?usage: check-commit-scope.sh <commit-msg-file>}"
+
+# First line that is not a comment or blank; git strips the comments later.
+subject="$(grep -v '^#' "$msg_file" | grep -m1 . || true)"
+
+# An empty message aborts the commit on git's side, so it is not this hook's
+# to complain about.
+[ -n "$subject" ] || exit 0
+
+# A revert or a merge git wrote itself is not the author's prose to police.
+case "$subject" in
+Revert\ * | Merge\ *) exit 0 ;;
+esac
+
+# type(scope)!: subject, where the scope is optional. The pattern is a
+# variable because bash's [[ ]] parser trips on an unquoted ")".
+full_re='^([a-z]+)(\(([^)]*)\))?!?: .+'
+if [[ ! "$subject" =~ $full_re ]]; then
+  {
+    echo "commit subject is not Conventional Commits:"
+    echo "  $subject"
+    echo
+    echo "Write:  type(scope): what changed"
+    echo "        type: what changed"
+    echo
+    # shellcheck disable=SC2086
+    echo "Types:  $(printf '%s, ' $TYPES | sed 's/, $//')"
+    echo "Scopes: $EPIC_SCOPES $NON_EPIC_SCOPES"
+  } >&2
+  exit 1
+fi
+
+type="${BASH_REMATCH[1]}"
+scopes="${BASH_REMATCH[3]}"
+
+case " $TYPES " in
+*" $type "*) ;;
+*)
+  {
+    echo "unknown commit type: $type"
+    echo
+    # shellcheck disable=SC2086
+    printf '  %s\n' $TYPES | sort
+  } >&2
+  exit 1
+  ;;
+esac
+
+# No scope is allowed: not every commit belongs to an epic.
+[ -n "$scopes" ] || exit 0
+
+known="$EPIC_SCOPES $NON_EPIC_SCOPES"
+bad=""
+IFS=',' read -ra parts <<<"$scopes"
+for scope in "${parts[@]}"; do
+  scope="$(printf '%s' "$scope" | tr -d '[:space:]')"
+  [ -n "$scope" ] || continue
+  case " $known " in
+  *" $scope "*) ;;
+  *) bad="$bad $scope" ;;
+  esac
+done
+
+[ -n "$bad" ] || exit 0
+
+{
+  echo "commit scope is not an epic or a known non-epic:$bad"
+  echo
+  echo "A scope names the epic in headquarters' plan/ that the work belongs"
+  echo "to, so a commit is findable from it. Use one of:"
+  echo
+  # shellcheck disable=SC2086
+  printf '  %s\n' $known | sort -u
+  echo
+  echo "or drop the scope. If a new epic exists in headquarters, add its id"
+  echo "to EPIC_SCOPES in this script."
+} >&2
+exit 1