diff --git a/.claude/settings.json b/.claude/settings.json
new file mode 100644
index 0000000..ccd6125
--- /dev/null
+++ b/.claude/settings.json
@@ -0,0 +1,17 @@
+{
+  "hooks": {
+    "PostToolUse": [
+      {
+        "matcher": "Write|Edit|MultiEdit|Bash",
+        "hooks": [
+          {
+            "type": "command",
+            "command": "/usr/bin/env bb \"$CLAUDE_PROJECT_DIR\"/scripts/agent-hooks/lint_format_check_hook.clj",
+            "async": true,
+            "timeout": 300
+          }
+        ]
+      }
+    ]
+  }
+}
diff --git a/.codex/hooks.json b/.codex/hooks.json
new file mode 100644
index 0000000..5f23d89
--- /dev/null
+++ b/.codex/hooks.json
@@ -0,0 +1,17 @@
+{
+  "hooks": {
+    "PostToolUse": [
+      {
+        "matcher": "Bash",
+        "hooks": [
+          {
+            "type": "command",
+            "command": "/usr/bin/env bb \"$(git rev-parse --show-toplevel)/scripts/agent-hooks/lint_format_check_hook.clj\"",
+            "statusMessage": "Running ceeker format-check and lint",
+            "timeout": 300
+          }
+        ]
+      }
+    ]
+  }
+}
diff --git a/Makefile b/Makefile
index 11a2512..6fb7635 100644
--- a/Makefile
+++ b/Makefile
@@ -1,6 +1,6 @@
-.PHONY: test test-install-script lint format-check format ci run clean uber
+.PHONY: test test-install-script test-agent-hooks lint format-check format ci run clean uber
 
-test: test-install-script
+test: test-install-script test-agent-hooks
 	mkdir -p target/test-runtime
 	mkdir -p target/test-runtime/tmux
 	TMUX= TMUX_PANE= TMUX_TMPDIR=$(CURDIR)/target/test-runtime/tmux XDG_RUNTIME_DIR=$(CURDIR)/target/test-runtime clojure -M:test
@@ -8,6 +8,9 @@ test: test-install-script
 test-install-script:
 	sh test/install_script_test.sh
 
+test-agent-hooks:
+	sh test/agent_hook_test.sh
+
 lint:
 	clojure -M:lint
 
diff --git a/README.ja.md b/README.ja.md
index 6161355..8c4f890 100644
--- a/README.ja.md
+++ b/README.ja.md
@@ -418,6 +418,15 @@ make lint
 make format
 ```
 
+ceeker repo には、Claude Code と Codex 向けの repo-local hook 設定を同梱しています。
+
+- `.claude/settings.json`: `Write|Edit|MultiEdit|Bash` の `PostToolUse` 後に `scripts/agent-hooks/lint_format_check_hook.clj` を非同期実行
+- `.codex/hooks.json`: `PostToolUse` 後に同じスクリプトを実行
+
+この hook は babashka (`bb`) で動作し、`make format-check` と `make lint` を順に実行して結果を agent に返します。Claude Code は repo を開くだけで有効です。Codex は feature flag が必要なので、未設定なら `~/.codex/config.toml` に `[features] codex_hooks = true` を追加するか `codex features enable codex_hooks` を実行してください。
+
+補足: Codex の `PostToolUse` は 2026-04-14 時点の公式仕様では `Bash` のみが発火対象です。そのため ceeker の Codex hook も、ファイル変更の可能性がある Bash 実行に対してのみ `format-check` / `lint` を走らせます。
+
 ## CI
 
 GitHub Actions で以下のジョブが PR / main push 時に実行されます:
diff --git a/README.md b/README.md
index acca111..eed0108 100644
--- a/README.md
+++ b/README.md
@@ -418,6 +418,15 @@ make lint
 make format
 ```
 
+The ceeker repo ships repo-local hooks for both Claude Code and Codex.
+
+- `.claude/settings.json`: runs `scripts/agent-hooks/lint_format_check_hook.clj` asynchronously after `PostToolUse` for `Write|Edit|MultiEdit|Bash`
+- `.codex/hooks.json`: runs the same script after `PostToolUse`
+
+The hook is implemented as a babashka (`bb`) script. It runs `make format-check` and `make lint` in sequence and reports the result back to the agent. Claude Code picks this up automatically when you open the repo. For Codex, ensure the feature flag is enabled by adding `[features] codex_hooks = true` to `~/.codex/config.toml` or by running `codex features enable codex_hooks`.
+
+Note: per the official Codex hooks documentation as of April 14, 2026, `PostToolUse` currently fires only for `Bash`. ceeker therefore limits the Codex hook to Bash commands that are likely to have modified the workspace before running `format-check` and `lint`.
+
 ## CI
 
 GitHub Actions runs the following jobs on PRs and pushes to main:
diff --git a/scripts/agent-hooks/lint_format_check_hook.clj b/scripts/agent-hooks/lint_format_check_hook.clj
new file mode 100644
index 0000000..8c91034
--- /dev/null
+++ b/scripts/agent-hooks/lint_format_check_hook.clj
@@ -0,0 +1,110 @@
+#!/usr/bin/env bb
+
+(ns lint-format-check-hook
+  (:require [cheshire.core :as json]
+            [clojure.java.shell :as sh]
+            [clojure.string :as str]))
+
+(def edit-tools #{"Write" "Edit" "MultiEdit"})
+
+(def validation-commands
+  #{"make lint"
+    "make format-check"
+    "make ci"
+    "clojure -M:lint"
+    "clojure -M:format-check"
+    "clojure -M:test"})
+
+(def mutating-bash-patterns
+  [#"\bapply_patch\b"
+   #"\bgit\s+apply\b"
+   #"\bpatch\b"
+   #"\bsed\s+-i\b"
+   #"\bperl\s+-pi\b"
+   #"\bmv\b"
+   #"\bcp\b"
+   #"\brm\b"
+   #"\bmkdir\b"
+   #"\btouch\b"
+   #"\btee\b"
+   #"\bchmod\b"
+   #"\bchown\b"
+   #">>"
+   #"(^|[^>])>([^>]|$)"])
+
+(defn read-payload []
+  (let [raw (str/trim (slurp *in*))]
+    (if (str/blank? raw)
+      {}
+      (json/parse-string raw true))))
+
+(defn normalize-command [command]
+  (->> (str/split (str/trim command) #"\s+")
+       (remove str/blank?)
+       (str/join " ")))
+
+(defn should-run [payload]
+  (if (not= "PostToolUse" (:hook_event_name payload))
+    [false nil]
+    (let [tool-name (str (:tool_name payload))
+          command (str (get-in payload [:tool_input :command] ""))
+          normalized-command (normalize-command command)]
+      (cond
+        (contains? edit-tools tool-name)
+        [true tool-name]
+
+        (not= "Bash" tool-name)
+        [false nil]
+
+        (contains? validation-commands normalized-command)
+        [false nil]
+
+        (some #(re-find % command) mutating-bash-patterns)
+        [true "Bash command"]
+
+        :else
+        [false nil]))))
+
+(defn summarize-output [output]
+  (let [trimmed (str/trim output)]
+    (if (str/blank? trimmed)
+      ""
+      (let [summary (->> (str/split-lines trimmed)
+                         (take 20)
+                         (str/join "\n"))]
+        (if (> (count summary) 2000)
+          (str (subs summary 0 2000) "\n...")
+          summary)))))
+
+(defn run-target [target]
+  (let [{:keys [exit out err]} (sh/sh "make" target)
+        combined (->> [out err]
+                      (map str/trim)
+                      (remove str/blank?)
+                      (str/join "\n"))]
+    [(zero? exit) combined]))
+
+(defn emit-message [message]
+  (println (json/generate-string {:systemMessage message})))
+
+(defn failure-message [target trigger output]
+  (let [summary (summarize-output output)
+        message (str target " failed after " trigger ".")]
+    (if (str/blank? summary)
+      message
+      (str message "\n" summary))))
+
+(defn -main []
+  (let [payload (read-payload)
+        [should-validate trigger] (should-run payload)]
+    (when should-validate
+      (let [[format-ok format-output] (run-target "format-check")]
+        (if-not format-ok
+          (emit-message (failure-message "format-check" trigger format-output))
+          (let [[lint-ok lint-output] (run-target "lint")]
+            (if lint-ok
+              (emit-message (str "format-check and lint passed after " trigger "."))
+              (emit-message (failure-message "lint" trigger lint-output))))))))
+  0)
+
+(System/exit (-main))
diff --git a/test/agent_hook_test.sh b/test/agent_hook_test.sh
new file mode 100644
index 0000000..7a649fa
--- /dev/null
+++ b/test/agent_hook_test.sh
@@ -0,0 +1,173 @@
+#!/usr/bin/env sh
+set -eu
+
+REPO_ROOT=$(CDPATH= cd -- "$(dirname "$0")/.." && pwd)
+HOOK_SCRIPT="${REPO_ROOT}/scripts/agent-hooks/lint_format_check_hook.clj"
+TEST_TMP_ROOT=$(mktemp -d)
+PASS_COUNT=0
+FAIL_COUNT=0
+
+cleanup() {
+  rm -rf "${TEST_TMP_ROOT}"
+}
+
+pass() {
+  PASS_COUNT=$((PASS_COUNT + 1))
+  printf 'PASS %s\n' "$1"
+}
+
+fail() {
+  FAIL_COUNT=$((FAIL_COUNT + 1))
+  printf 'FAIL %s: %s\n' "$1" "$2" >&2
+}
+
+assert_contains() {
+  file_path="$1"
+  expected="$2"
+  label="$3"
+  if ! grep -F "$expected" "$file_path" >/dev/null 2>&1; then
+    fail "$label" "expected '$expected' in $file_path"
+    return 1
+  fi
+  return 0
+}
+
+assert_empty() {
+  file_path="$1"
+  label="$2"
+  if [ -s "$file_path" ]; then
+    fail "$label" "expected empty file: $file_path"
+    return 1
+  fi
+  return 0
+}
+
+assert_line_count() {
+  file_path="$1"
+  expected="$2"
+  label="$3"
+  actual=$(wc -l <"$file_path" | tr -d ' ')
+  if [ "$actual" != "$expected" ]; then
+    fail "$label" "expected $expected lines in $file_path, got $actual"
+    return 1
+  fi
+  return 0
+}
+
+setup_case() {
+  CASE_DIR="${TEST_TMP_ROOT}/$1"
+  STUB_DIR="${CASE_DIR}/bin"
+  LOG_FILE="${CASE_DIR}/make.log"
+  OUTPUT_FILE="${CASE_DIR}/stdout.json"
+  INPUT_FILE="${CASE_DIR}/input.json"
+  MAKE_BEHAVIOR="${CASE_DIR}/make-behavior"
+
+  mkdir -p "${STUB_DIR}"
+  : >"${LOG_FILE}"
+  : >"${OUTPUT_FILE}"
+  : >"${MAKE_BEHAVIOR}"
+
+  cat >"${STUB_DIR}/make" <<'EOF'
+#!/usr/bin/env sh
+set -eu
+printf '%s\n' "$*" >> "${HOOK_TEST_MAKE_LOG}"
+
+if [ -f "${HOOK_TEST_MAKE_BEHAVIOR}" ]; then
+  while IFS='=' read -r key value; do
+    [ -n "${key}" ] || continue
+    if [ "$1" = "${key}" ]; then
+      if [ "${value}" = "0" ]; then
+        printf '%s ok\n' "$1"
+        exit 0
+      fi
+      printf '%s failed\n' "$1" >&2
+      exit "${value}"
+    fi
+  done < "${HOOK_TEST_MAKE_BEHAVIOR}"
+fi
+
+printf '%s ok\n' "$1"
+EOF
+  chmod +x "${STUB_DIR}/make"
+}
+
+run_hook() {
+  payload="$1"
+  printf '%s\n' "$payload" >"${INPUT_FILE}"
+  HOOK_TEST_MAKE_LOG="${LOG_FILE}" \
+  HOOK_TEST_MAKE_BEHAVIOR="${MAKE_BEHAVIOR}" \
+  PATH="${STUB_DIR}:${PATH}" \
+  bb "${HOOK_SCRIPT}" <"${INPUT_FILE}" >"${OUTPUT_FILE}"
+}
+
+test_write_runs_format_and_lint() {
+  setup_case "write-runs-checks"
+
+  if run_hook '{"hook_event_name":"PostToolUse","tool_name":"Write","tool_input":{"file_path":"src/ceeker/core.clj"}}'; then
+    assert_line_count "${LOG_FILE}" 2 "write runs both make targets" || return 1
+    assert_contains "${LOG_FILE}" "format-check" "write runs format-check first" || return 1
+    assert_contains "${LOG_FILE}" "lint" "write runs lint second" || return 1
+    assert_contains "${OUTPUT_FILE}" "format-check and lint passed after Write" "write pass message" || return 1
+    pass "Write tool triggers format-check and lint"
+    return 0
+  fi
+
+  fail "Write tool triggers format-check and lint" "hook command failed"
+  return 1
+}
+
+test_read_only_bash_skips_checks() {
+  setup_case "bash-skip"
+
+  if run_hook '{"hook_event_name":"PostToolUse","tool_name":"Bash","tool_input":{"command":"rg hook README.md"}}'; then
+    assert_empty "${LOG_FILE}" "read-only bash should skip make" || return 1
+    assert_empty "${OUTPUT_FILE}" "read-only bash should not emit message" || return 1
+    pass "read-only Bash command skips checks"
+    return 0
+  fi
+
+  fail "read-only Bash command skips checks" "hook command failed"
+  return 1
+}
+
+test_mutating_bash_runs_checks() {
+  setup_case "bash-runs-checks"
+
+  if run_hook '{"hook_event_name":"PostToolUse","tool_name":"Bash","tool_input":{"command":"git apply /tmp/change.patch"}}'; then
+    assert_line_count "${LOG_FILE}" 2 "mutating bash runs both make targets" || return 1
+    assert_contains "${OUTPUT_FILE}" "format-check and lint passed after Bash command" "bash pass message" || return 1
+    pass "mutating Bash command triggers checks"
+    return 0
+  fi
+
+  fail "mutating Bash command triggers checks" "hook command failed"
+  return 1
+}
+
+test_format_check_failure_reports_message() {
+  setup_case "format-failure"
+  printf 'format-check=1\n' >"${MAKE_BEHAVIOR}"
+
+  if run_hook '{"hook_event_name":"PostToolUse","tool_name":"Edit","tool_input":{"file_path":"src/ceeker/core.clj"}}'; then
+    assert_line_count "${LOG_FILE}" 1 "format-check failure should stop before lint" || return 1
+    assert_contains "${OUTPUT_FILE}" "format-check failed after Edit" "format failure message" || return 1
+    assert_contains "${OUTPUT_FILE}" "format-check failed" "format failure output" || return 1
+    pass "format-check failure is reported"
+    return 0
+  fi
+
+  fail "format-check failure is reported" "hook command failed"
+  return 1
+}
+
+test_write_runs_format_and_lint
+test_read_only_bash_skips_checks
+test_mutating_bash_runs_checks
+test_format_check_failure_reports_message
+
+if [ "${FAIL_COUNT}" -ne 0 ]; then
+  printf '%s test(s) failed\n' "${FAIL_COUNT}" >&2
+  exit 1
+fi
+
+printf '%s test(s) passed\n' "${PASS_COUNT}"