diff --git a/include/ruby/thread.h b/include/ruby/thread.h
index f11cc19086..496f026334 100644
--- a/include/ruby/thread.h
+++ b/include/ruby/thread.h
@@ -267,6 +267,46 @@ rb_internal_thread_event_hook_t *rb_internal_thread_add_event_hook(
 bool rb_internal_thread_remove_event_hook(
         rb_internal_thread_event_hook_t * hook);
 
+
+typedef int rb_internal_thread_specific_key_t;
+#define RB_INTERNAL_THREAD_SPECIFIC_KEY_MAX 8
+/**
+ * Create a key to store thread specific data.
+ *
+ * These APIs are designed for tools using
+ * rb_internal_thread_event_hook APIs.
+ *
+ * Note that only `RB_INTERNAL_THREAD_SPECIFIC_KEY_MAX` keys
+ * can be created. raises `ThreadError` if exceeded.
+ *
+ * Usage:
+ *   // at initialize time:
+ *   int tool_key; // gvar
+ *   Init_tool() {
+ *     tool_key = rb_internal_thread_specific_key_create();
+ *   }
+ *
+ *   // at any timing:
+ *   rb_internal_thread_pecific_set(thread, tool_key, per_thread_data);
+ *   ...
+ *   per_thread_data = rb_internal_thread_specific_get(thread, tool_key);
+ */
+rb_internal_thread_specific_key_t rb_internal_thread_specific_key_create(void);
+
+/**
+ * Get thread and tool specific data.
+ *
+ * This function is async signal safe and thread safe.
+ */
+void *rb_internal_thread_specific_get(VALUE thread_val, rb_internal_thread_specific_key_t key);
+
+/**
+ * Set thread and tool specific data.
+ *
+ * This function is async signal safe and thread safe.
+ */
+void rb_internal_thread_specific_set(VALUE thread_val, rb_internal_thread_specific_key_t key, void *data);
+
 RBIMPL_SYMBOL_EXPORT_END()
 
 #endif /* RUBY_THREAD_H */
diff --git a/rjit_c.rb b/rjit_c.rb
index 7e00fad9b4..4606352a96 100644
--- a/rjit_c.rb
+++ b/rjit_c.rb
@@ -1530,6 +1530,7 @@ module RubyVM::RJIT # :nodoc: all
       scheduler: [self.VALUE, Primitive.cexpr!("OFFSETOF((*((struct rb_thread_struct *)NULL)), scheduler)")],
       blocking: [CType::Immediate.parse("unsigned int"), Primitive.cexpr!("OFFSETOF((*((struct rb_thread_struct *)NULL)), blocking)")],
       name: [self.VALUE, Primitive.cexpr!("OFFSETOF((*((struct rb_thread_struct *)NULL)), name)")],
+      specific_storage: [CType::Pointer.new { CType::Pointer.new { CType::Immediate.parse("void") } }, Primitive.cexpr!("OFFSETOF((*((struct rb_thread_struct *)NULL)), specific_storage)")],
       ext_config: [self.rb_ext_config, Primitive.cexpr!("OFFSETOF((*((struct rb_thread_struct *)NULL)), ext_config)")],
     )
   end
diff --git a/thread.c b/thread.c
index 1e160d6ab9..3e9493ae3c 100644
--- a/thread.c
+++ b/thread.c
@@ -149,6 +149,7 @@ NORETURN(static void async_bug_fd(const char *mesg, int errno_arg, int fd));
 static int consume_communication_pipe(int fd);
 
 static volatile int system_working = 1;
+static rb_internal_thread_specific_key_t specific_key_count;
 
 struct waiting_fd {
     struct ccan_list_node wfd_node; /* <=> vm.waiting_fds */
@@ -778,6 +779,8 @@ struct thread_create_params {
     VALUE (*fn)(void *);
 };
 
+static void thread_specific_storage_alloc(rb_thread_t *th);
+
 static VALUE
 thread_create_core(VALUE thval, struct thread_create_params *params)
 {
@@ -785,6 +788,8 @@ thread_create_core(VALUE thval, struct thread_create_params *params)
     rb_thread_t *th = rb_thread_ptr(thval), *current_th = rb_ec_thread_ptr(ec);
     int err;
 
+    thread_specific_storage_alloc(th);
+
     if (OBJ_FROZEN(current_th->thgroup)) {
         rb_raise(rb_eThreadError,
                  "can't start a new thread (frozen ThreadGroup)");
@@ -5783,3 +5788,66 @@ rb_uninterruptible(VALUE (*b_proc)(VALUE), VALUE data)
     RUBY_VM_CHECK_INTS(cur_th->ec);
     return ret;
 }
+
+static void
+thread_specific_storage_alloc(rb_thread_t *th)
+{
+    VM_ASSERT(th->specific_storage == NULL);
+
+    if (UNLIKELY(specific_key_count > 0)) {
+        th->specific_storage = ZALLOC_N(void *, RB_INTERNAL_THREAD_SPECIFIC_KEY_MAX);
+    }
+}
+
+rb_internal_thread_specific_key_t
+rb_internal_thread_specific_key_create(void)
+{
+    rb_vm_t *vm = GET_VM();
+
+    if (specific_key_count == 0 && vm->ractor.cnt > 1) {
+        rb_raise(rb_eThreadError, "The first rb_internal_thread_specific_key_create() is called with multiple ractors");
+    }
+    else if (specific_key_count > RB_INTERNAL_THREAD_SPECIFIC_KEY_MAX) {
+        rb_raise(rb_eThreadError, "rb_internal_thread_specific_key_create() is called more than %d times", RB_INTERNAL_THREAD_SPECIFIC_KEY_MAX);
+    }
+    else {
+        rb_internal_thread_specific_key_t key = specific_key_count++;
+
+        if (key == 0) {
+            // allocate
+            rb_ractor_t *cr = GET_RACTOR();
+            rb_thread_t *th;
+
+            ccan_list_for_each(&cr->threads.set, th, lt_node) {
+                thread_specific_storage_alloc(th);
+            }
+        }
+        return key;
+    }
+}
+
+// async and native thread safe.
+void *
+rb_internal_thread_specific_get(VALUE thread_val, rb_internal_thread_specific_key_t key)
+{
+    rb_thread_t *th = DATA_PTR(thread_val);
+
+    VM_ASSERT(rb_thread_ptr(thread_val) == th);
+    VM_ASSERT(key < RB_INTERNAL_THREAD_SPECIFIC_KEY_MAX);
+    VM_ASSERT(th->specific_storage);
+
+    return th->specific_storage[key];
+}
+
+// async and native thread safe.
+void
+rb_internal_thread_specific_set(VALUE thread_val, rb_internal_thread_specific_key_t key, void *data)
+{
+    rb_thread_t *th = DATA_PTR(thread_val);
+
+    VM_ASSERT(rb_thread_ptr(thread_val) == th);
+    VM_ASSERT(key < RB_INTERNAL_THREAD_SPECIFIC_KEY_MAX);
+    VM_ASSERT(th->specific_storage);
+
+    th->specific_storage[key] = data;
+}
diff --git a/vm.c b/vm.c
index 294ee389aa..d7ae74a968 100644
--- a/vm.c
+++ b/vm.c
@@ -3435,6 +3435,10 @@ thread_free(void *ptr)
         rb_bug("thread_free: keeping_mutexes must be NULL (%p:%p)", (void *)th, (void *)th->keeping_mutexes);
     }
 
+    if (th->specific_storage) {
+        ruby_xfree(th->specific_storage);
+    }
+
     rb_threadptr_root_fiber_release(th);
 
     if (th->vm && th->vm->ractor.main_thread == th) {
diff --git a/vm_core.h b/vm_core.h
index fcac71b2e5..cd720fd8cf 100644
--- a/vm_core.h
+++ b/vm_core.h
@@ -1152,6 +1152,7 @@ typedef struct rb_thread_struct {
 
     /* misc */
     VALUE name;
+    void **specific_storage;
 
     struct rb_ext_config ext_config;
 } rb_thread_t;