diff --git a/src/Lean/Server/References.lean b/src/Lean/Server/References.lean
new file mode 100644
index 0000000000..98bde40c96
--- /dev/null
+++ b/src/Lean/Server/References.lean
@@ -0,0 +1,75 @@
+import Lean.Data.Json
+import Lean.Data.Lsp
+
+namespace Lean.Server.References
+open Std
+open Lsp
+
+inductive RefIdent where
+  | const : Name → RefIdent
+  | fvar : FVarId → RefIdent
+  deriving BEq, Hashable
+
+namespace RefIdent
+
+def toString : RefIdent → String
+  | RefIdent.const n => s!"c:{n}"
+  | RefIdent.fvar id => s!"f:{id.name}"
+
+def fromString (s : String) : Except String RefIdent := do
+  let sPrefix := s.take 2
+  let sName := s.drop 2
+  let mk ← match sPrefix with
+    | "c:" => RefIdent.const
+    | "f:" => fun n => RefIdent.fvar <| FVarId.mk n
+    | _ => throw "string must start with 'c:' or 'f:'"
+  -- See `FromJson Name`
+  let name ← match sName with
+    | "[anonymous]" => Name.anonymous
+    | _ => match Syntax.decodeNameLit ("`" ++ sName) with
+      | some n => n
+      | none => throw s!"expected a Name, got {sName}"
+  mk name
+
+end RefIdent
+
+structure RefInfo where
+  definition : Option Lsp.Range
+  usages : Array Lsp.Range
+
+instance : ToJson RefInfo where
+  toJson i :=
+    let rangeToList (r : Lsp.Range) : List Nat :=
+      [r.start.line, r.start.character, r.end.line, r.end.character]
+    Json.mkObj [
+      ("definition", toJson $ i.definition.map rangeToList),
+      ("usages", toJson $ i.usages.map rangeToList)
+    ]
+
+instance : FromJson RefInfo where
+  fromJson? j := do
+    let listToRange (l : List Nat) : Except String Lsp.Range := match l with
+      | [sLine, sChar, eLine, eChar] => pure ⟨⟨sLine, sChar⟩, ⟨eLine, eChar⟩⟩
+      | _ => throw s!"Expected list of length 4, not {l.length}"
+    let definition ← j.getObjValAs? (Option $ List Nat) "definition"
+    let definition ← match definition with
+      | none => pure none
+      | some list => some <$> listToRange list
+    let usages ← j.getObjValAs? (Array $ List Nat) "usages"
+    let usages ← usages.mapM listToRange
+    pure { definition, usages }
+
+def FileRefMap := HashMap RefIdent RefInfo
+
+instance : ToJson FileRefMap where
+  toJson m := Json.mkObj <| m.toList.map fun (ident, info) => (ident.toString, toJson info)
+
+instance : FromJson FileRefMap where
+  fromJson? j := do
+    let node ← j.getObj?
+    node.foldM (init := HashMap.empty) fun m k v => do
+      m.insert (← RefIdent.fromString k) (← fromJson? v)
+
+def RefMap := HashMap String FileRefMap
+
+end Lean.Server.References