diff --git a/DocGen4/Output.lean b/DocGen4/Output.lean
index ae4037e..4e3f32d 100644
--- a/DocGen4/Output.lean
+++ b/DocGen4/Output.lean
@@ -127,17 +127,21 @@ def getSimpleBaseContext (hierarchy : Hierarchy) : IO SiteBaseContext := do
 def htmlOutputIndex (baseConfig : SiteBaseContext) : IO Unit := do
   htmlOutputSetup baseConfig
 
-  let mut index : JsonIndex := { }
-  for entry in ←System.FilePath.readDir declarationsBasePath do
+  let mut index : JsonIndex := {}
+  let mut headerIndex : JsonHeaderIndex := {}
+  for entry in ← System.FilePath.readDir declarationsBasePath do
     if entry.fileName.startsWith "declaration-data-" && entry.fileName.endsWith ".bmp" then
       let fileContent ← FS.readFile entry.path
       let .ok jsonContent := Json.parse fileContent | unreachable!
       let .ok (module : JsonModule) := fromJson? jsonContent | unreachable!
       index := index.addModule module |>.run baseConfig
+      headerIndex := headerIndex.addModule module
 
   let finalJson := toJson index
+  let finalHeaderJson := toJson headerIndex
   -- The root JSON for find
   FS.writeFile (declarationsBasePath / "declaration-data.bmp") finalJson.compress
+  FS.writeFile (declarationsBasePath / "header-data.bmp") finalHeaderJson.compress
 
 /--
 The main entrypoint for outputting the documentation HTML based on an
diff --git a/DocGen4/Output/ToJson.lean b/DocGen4/Output/ToJson.lean
index 155e3cf..3fc7ff2 100644
--- a/DocGen4/Output/ToJson.lean
+++ b/DocGen4/Output/ToJson.lean
@@ -1,20 +1,27 @@
 import Lean
 import DocGen4.Process
 import DocGen4.Output.Base
+import DocGen4.Output.Module
 import Lean.Data.RBMap
 
 namespace DocGen4.Output
 
 open Lean
 
-structure JsonDeclaration where
+structure JsonDeclarationInfo where
   name : String
   kind : String
   doc : String
   docLink : String
   sourceLink : String
+  line : Nat
   deriving FromJson, ToJson
 
+structure JsonDeclaration where
+  info : JsonDeclarationInfo
+  header : String
+deriving FromJson, ToJson
+
 structure JsonInstance where
   name : String
   className : String
@@ -28,13 +35,19 @@ structure JsonModule where
   imports : Array String
   deriving FromJson, ToJson
 
+structure JsonHeaderIndex where
+  headers : List (String × String) := []
+
 structure JsonIndex where
-  declarations : List (String × JsonDeclaration) := []
+  declarations : List (String × JsonDeclarationInfo) := []
   instances : HashMap String (RBTree String Ord.compare) := .empty
   importedBy : HashMap String (Array String) := .empty
   modules : List (String × String) := []
   instancesFor : HashMap String (RBTree String Ord.compare) := .empty
 
+instance : ToJson JsonHeaderIndex where
+  toJson idx := Json.mkObj <| idx.headers.map (fun (k, v) => (k, toJson v))
+
 instance : ToJson JsonIndex where
   toJson idx := Id.run do
     let jsonDecls := Json.mkObj <| idx.declarations.map (fun (k, v) => (k, toJson v))
@@ -51,10 +64,14 @@ instance : ToJson JsonIndex where
     ]
     return finalJson
 
+def JsonHeaderIndex.addModule (index : JsonHeaderIndex) (module : JsonModule) : JsonHeaderIndex :=
+  let merge idx decl := { idx with headers := (decl.info.name, decl.header) :: idx.headers }
+  module.declarations.foldl merge index
+
 def JsonIndex.addModule (index : JsonIndex) (module : JsonModule) : BaseHtmlM JsonIndex := do
   let mut index := index
   let newModule := (module.name, ← moduleNameToLink (String.toName module.name))
-  let newDecls := module.declarations.map (fun d => (d.name, d))
+  let newDecls := module.declarations.map (fun d => (d.info.name, d.info))
   index := { index with
     modules := newModule :: index.modules
     declarations := newDecls ++ index.declarations
@@ -81,7 +98,10 @@ def DocInfo.toJson (module : Name) (info : Process.DocInfo) : HtmlM JsonDeclarat
   let doc := info.getDocString.getD ""
   let docLink ← declNameToLink info.getName
   let sourceLink ← getSourceUrl module info.getDeclarationRange
-  return { name, kind, doc, docLink, sourceLink }
+  let line := info.getDeclarationRange.pos.line
+  let header := (← docInfoHeader info).toString
+  let info := { name, kind, doc, docLink, sourceLink, line }
+  return { info, header }
 
 def Process.Module.toJson (module : Process.Module) : HtmlM Json := do
     let mut jsonDecls := []