diff --git a/src/rime/candidate.h b/src/rime/candidate.h
index 2f75dcfec9..1a09deeec1 100644
--- a/src/rime/candidate.h
+++ b/src/rime/candidate.h
@@ -41,11 +41,29 @@ class Candidate {
   void set_end(size_t end) { end_ = end; }
   void set_quality(double quality) { quality_ = quality; }
 
+  // per-candidate data
+  void set_data(const string& data_tag, an<void> datum = nullptr) {
+    data_[data_tag] = datum;
+  }
+  an<void> get_data(const string& data_tag) const {
+    auto it = data_.find(data_tag);
+    return it != data_.end() ? it->second : nullptr;
+  }
+  vector<string> get_data_keys() const {
+    vector<string> keys;
+    keys.reserve(data_.size());
+    for (const auto& pair : data_) {
+      keys.push_back(pair.first);
+    }
+    return keys;
+  }
+
  private:
   string type_;
   size_t start_ = 0;
   size_t end_ = 0;
   double quality_ = 0.;
+  hash_map<string, an<void>> data_;
 };
 
 using CandidateQueue = list<of<Candidate>>;