How to Make a Save System in Unity with JSON

1. Put the saved state in one class

Don't save GameObjects or MonoBehaviours. Save plain data: numbers, strings, vectors and lists. One class keeps it easy to version later.

using UnityEngine;

[System.Serializable]
public class SaveData
{
    public int version = 1;
    public int coins;
    public Vector3 checkpoint;
    public Color playerColor = Color.white;
}

2. Write and read the file

Application.persistentDataPath points to a folder that survives updates on every platform. Write to a temporary file first and then swap it in, so a crash mid-write never corrupts the player's save.

using System.IO;
using UnityEngine;

public static class SaveSystem
{
    static string FilePath => Path.Combine(Application.persistentDataPath, "save.json");

    public static void Save(SaveData data)
    {
        string tmp = FilePath + ".tmp";
        File.WriteAllText(tmp, JsonUtility.ToJson(data, true));
        if (File.Exists(FilePath)) File.Replace(tmp, FilePath, null);
        else File.Move(tmp, FilePath);
    }

    public static SaveData Load()
    {
        if (!File.Exists(FilePath)) return new SaveData();
        return JsonUtility.FromJson<SaveData>(File.ReadAllText(FilePath));
    }

    public static void Delete()
    {
        if (File.Exists(FilePath)) File.Delete(FilePath);
    }
}

3. JSON file or PlayerPrefs?

A common setup is both: JSON for the game, PlayerPrefs for settings. To store JSON in PlayerPrefs instead, call PlayerPrefs.SetString("save", json) and then PlayerPrefs.Save().

4. Decide when to save

• On events: picking up a coin, reaching a checkpoint, finishing a quest. Players never lose more than a moment.
• On quit: OnApplicationQuit, and OnApplicationPause(true) on mobile, where apps get killed without warning.
• Not every frame: disk writes are slow. Mark the data dirty and save once at the end of the frame or on a timer.

Keep the version field from step 1. When you add fields in an update, old saves still load: missing fields get their default values, and you can migrate based on the version number.

Skip the setup: a ready save system

The Save & Load System for Unity is this pattern finished: one controller, a JSON/PlayerPrefs checkbox, checkpoints, coins, colour platforms and a demo level, with full C# source. It pairs well with the Inventory System and the Character Customizer, which saves outfits the same way.

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10 Game Systems for Unity: Doors, Inventory, Save, Shop & RPG

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