diff --git a/clang-tools-extra/clangd/TUScheduler.cpp b/clang-tools-extra/clangd/TUScheduler.cpp
--- a/clang-tools-extra/clangd/TUScheduler.cpp
+++ b/clang-tools-extra/clangd/TUScheduler.cpp
@@ -143,10 +143,17 @@
   /// the cache anymore. If nullptr was cached for \p K, this function will
   /// return a null unique_ptr wrapped into an optional.
   llvm::Optional<std::unique_ptr<ParsedAST>> take(Key K) {
+    trace::Metric M("/clangd/ast_cache");
+    M.Ty = trace::Metric::Increment;
+    M.Value = 1;
+    // Record metric after unlocking the mutex.
     std::unique_lock<std::mutex> Lock(Mut);
     auto Existing = findByKey(K);
-    if (Existing == LRU.end())
+    if (Existing == LRU.end()) {
+      M.Labels = {"miss"};
       return None;
+    }
+    M.Labels = {"hit"};
     std::unique_ptr<ParsedAST> V = std::move(Existing->second);
     LRU.erase(Existing);
     // GCC 4.8 fails to compile `return V;`, as it tries to call the copy
diff --git a/clang-tools-extra/clangd/Trace.h b/clang-tools-extra/clangd/Trace.h
--- a/clang-tools-extra/clangd/Trace.h
+++ b/clang-tools-extra/clangd/Trace.h
@@ -18,14 +18,40 @@
 #define LLVM_CLANG_TOOLS_EXTRA_CLANGD_TRACE_H_
 
 #include "Context.h"
+#include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/Support/JSON.h"
 #include "llvm/Support/raw_ostream.h"
+#include <string>
+#include <vector>
 
 namespace clang {
 namespace clangd {
 namespace trace {
 
+/// Represents measurements of clangd events, e.g. operation latency. Reports
+/// itself to active tracer on destruction.
+struct Metric {
+  enum Type {
+    /// Occurence of an event, e.g. cache access.
+    Increment,
+    /// Aspect of an event, e.g. number of symbols in an index lookup.
+    Sample,
+  };
+  /// Uniquely identifies the metric.
+  const llvm::StringLiteral Name;
+  /// Divides a metric into meaningful parts. e.g. hit/miss to represent result
+  /// of a cache access.
+  std::vector<std::string> Labels;
+  double Value = 0;
+  Type Ty;
+
+  Metric(llvm::StringLiteral Name) : Name(Name) {}
+  Metric(const Metric &) = delete;
+  Metric &operator=(const Metric &) = delete;
+  ~Metric();
+};
+
 /// A consumer of trace events. The events are produced by Spans and trace::log.
 /// Implementations of this interface must be thread-safe.
 class EventTracer {
@@ -47,6 +73,9 @@
 
   /// Called for instant events.
   virtual void instant(llvm::StringRef Name, llvm::json::Object &&Args) = 0;
+
+  /// Called whenever an event exports a measurement.
+  virtual void record(const Metric &Metric) {}
 };
 
 /// Sets up a global EventTracer that consumes events produced by Span and
diff --git a/clang-tools-extra/clangd/Trace.cpp b/clang-tools-extra/clangd/Trace.cpp
--- a/clang-tools-extra/clangd/Trace.cpp
+++ b/clang-tools-extra/clangd/Trace.cpp
@@ -149,10 +149,10 @@
   void rawEvent(llvm::StringRef Phase,
                 const llvm::json::Object &Event) /*REQUIRES(Mu)*/ {
     // PID 0 represents the clangd process.
-    Out.object([&]{
+    Out.object([&] {
       Out.attribute("pid", 0);
       Out.attribute("ph", Phase);
-      for (const auto& KV : Event)
+      for (const auto &KV : Event)
         Out.attribute(KV.first, KV.second);
     });
   }
@@ -230,6 +230,12 @@
     T->endSpan();
 }
 
+Metric::~Metric() {
+  if (!T)
+    return;
+  T->record(*this);
+}
+
 } // namespace trace
 } // namespace clangd
 } // namespace clang