diff --git a/types/sharedb/index.d.ts b/types/sharedb/index.d.ts
index 7657075f8e..2f78d1d3dc 100644
--- a/types/sharedb/index.d.ts
+++ b/types/sharedb/index.d.ts
@@ -125,8 +125,9 @@ declare namespace middleware {
         doc: DocContext;  // Deprecated, use 'readSnapshots' instead.
         op: OpContext;
         query: QueryContext;
-        receive: ReceiveContext;
         readSnapshots: ReadSnapshotsContext;
+        receive: ReceiveContext;
+        reply: ReplyContext;
         submit: SubmitContext;
     }
 
@@ -165,22 +166,27 @@ declare namespace middleware {
         projection: Projection | undefined;
         fields: ProjectionFields | undefined;
         channel: string;
-        query: any;
-        options: any;
+        query: ShareDB.JSONObject;
+        options: ShareDB.JSONObject;
         db: sharedb.DB | null;
         snapshotProjection: Projection | null;
     }
 
-    interface ReceiveContext extends BaseContext {
-        data: any;
-    }
-
     interface ReadSnapshotsContext extends BaseContext {
         collection: string;
         snapshots: ShareDB.Snapshot[];
         snapshotType: SnapshotType;
     }
 
+    interface ReceiveContext extends BaseContext {
+        data: ShareDB.JSONObject;  // ClientRequest, but before any validation
+    }
+
+    interface ReplyContext extends BaseContext {
+        request: ShareDB.ClientRequest;
+        reply: ShareDB.JSONObject;
+    }
+
     type SnapshotType = 'current' | 'byVersion' | 'byTimestamp';
 
     interface SubmitContext extends BaseContext, SubmitRequest {
diff --git a/types/sharedb/lib/sharedb.d.ts b/types/sharedb/lib/sharedb.d.ts
index 169b7e6674..01eace14c6 100644
--- a/types/sharedb/lib/sharedb.d.ts
+++ b/types/sharedb/lib/sharedb.d.ts
@@ -1,18 +1,25 @@
 import { EventEmitter } from 'events';
 
+export type JSONValue = string | number | boolean | null | JSONObject | JSONArray;
+export interface JSONObject {
+  [name: string]: JSONValue;
+}
+export interface JSONArray extends Array<JSONValue> {}
+
 export type Path = ReadonlyArray<string|number>;
 export interface Snapshot {
     id: string;
     v: number;
     type: string | null;
-    data: any;  // JSON object, could be undefined
+    data: JSONObject | undefined;
     m: SnapshotMeta | null;
 }
 
 export interface SnapshotMeta {
     ctime: number;
     mtime: number;
-    [key: string]: any;
+    // Users can use server middleware to add additional metadata to snapshots.
+    [key: string]: JSONValue;
 }
 
 export interface AddNumOp { p: Path; na: number; }
@@ -95,3 +102,12 @@ export class Query extends EventEmitter {
     removeListener(event: QueryEvent, listener: (...args: any[]) => any): this;
     destroy(): void;
 }
+
+export type RequestAction = 'qf' | 'qs' | 'qu' | 'bf' | 'bs' | 'bu' | 'f' | 's' | 'u' | 'op' | 'nf' | 'nt';
+
+export interface ClientRequest {
+    /** Short name of the request's action */
+    a: RequestAction;
+
+    [propertyName: string]: JSONValue;
+}
diff --git a/types/sharedb/sharedb-tests.ts b/types/sharedb/sharedb-tests.ts
index a4e35d3507..da4e5ed948 100644
--- a/types/sharedb/sharedb-tests.ts
+++ b/types/sharedb/sharedb-tests.ts
@@ -101,6 +101,16 @@ backend.use('receive', (context, callback) => {
     );
     callback();
 });
+backend.use('reply', (context, callback) => {
+    console.log(
+        context.action,
+        context.agent,
+        context.backend,
+        context.request,
+        context.reply,
+    );
+    callback();
+});
 backend.use('readSnapshots', (context, callback) => {
     console.log(
         context.action,