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doc/mkdocs/docs/features/object_order.md

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+# Object Order
+
+The [JSON standard](https://tools.ietf.org/html/rfc8259.html) defines objects as "an unordered collection of zero or more name/value pairs". As such, an implementation does not need to preserve any specific order of object keys.
+
+The default type `nlohmann::json` uses a `std::map` to store JSON objects, and thus stores object keys **sorted alphabetically**.
+
+??? example
+
+    ```cpp
+    #include <iostream>
+    #include "json.hpp"
+    
+    using json = nlohmann::json;
+    
+    int main()
+    {
+        json j;
+        j["one"] = 1;
+        j["two"] = 2;
+        j["three"] = 3;
+        
+        std::cout << j.dump(2) << '\n';
+    }
+    ```
+    
+    Output:
+
+    ```json
+    {
+      "one": 1,
+      "three": 3,
+      "two": 2
+    }
+    ```
+
+If you do want to preserve the **insertion order**, you can try the type [`nlohmann::ordered_json`](https://github.com/nlohmann/json/issues/2179).
+
+??? example
+
+    ```cpp
+    #include <iostream>
+    #include <nlohmann/json.hpp>
+    
+    using ordered_json = nlohmann::ordered_json;
+    
+    int main()
+    {
+        ordered_json j;
+        j["one"] = 1;
+        j["two"] = 2;
+        j["three"] = 3;
+        
+        std::cout << j.dump(2) << '\n';
+    }
+    ```
+    
+    Output:
+    
+    ```json
+    {
+      "one": 1,
+      "two": 2,
+      "three": 3
+    }
+    ```
+
+Alternatively, you can use a more sophisticated ordered map like [`tsl::ordered_map`](https://github.com/Tessil/ordered-map) ([integration](https://github.com/nlohmann/json/issues/546#issuecomment-304447518)) or [`nlohmann::fifo_map`](https://github.com/nlohmann/fifo_map) ([integration](https://github.com/nlohmann/json/issues/485#issuecomment-333652309)).