Unity Project Guide: Save and Load a Checkpoint With JSON

Saving is one of the first systems that makes a prototype feel like a real game. This guide walks through a practical Unity save system using JSON.

You will save:

• Player position
• Player health
• Last checkpoint id
• Simple inventory item ids

This is not the final save architecture for every game, but it is a strong beginner-friendly foundation.

Step 1: Decide What Should Be Saved

Beginners often try to save entire GameObjects. Avoid that.

Save small, stable data:

1Good to save:2- player position3- health number4- item ids5- quest ids6- checkpoint ids7 8Bad to save:9- GameObject references10- Transform components11- Sprite objects12- MonoBehaviour instances

GameObjects are runtime objects. Save data should be plain information that can be recreated.

Step 2: Create Save Data Classes

Create SaveData.cs.

1using System;2using System.Collections.Generic;3 4[Serializable]5public class SaveData6{7    public int version = 1;8    public PlayerSaveData player = new PlayerSaveData();9    public List<string> inventoryItemIds = new List<string>();10}11 12[Serializable]13public class PlayerSaveData14{15    public float x;16    public float y;17    public int health;18    public string checkpointId;19}

These classes are intentionally boring. Unity's JsonUtility works best with simple serializable fields.

Step 3: Create the Save Manager

Create SaveManager.cs.

1using System.IO;2using UnityEngine;3 4public class SaveManager : MonoBehaviour5{6    public static SaveManager Instance { get; private set; }7 8    private string SavePath => Path.Combine(Application.persistentDataPath, "save.json");9 10    private void Awake()11    {12        if (Instance != null && Instance != this)13        {14            Destroy(gameObject);15            return;16        }17 18        Instance = this;19        DontDestroyOnLoad(gameObject);20    }21 22    public void Save(SaveData data)23    {24        string json = JsonUtility.ToJson(data, true);25        File.WriteAllText(SavePath, json);26        Debug.Log($"Saved to {SavePath}");27    }28 29    public bool TryLoad(out SaveData data)30    {31        data = null;32 33        if (!File.Exists(SavePath))34        {35            return false;36        }37 38        string json = File.ReadAllText(SavePath);39        data = JsonUtility.FromJson<SaveData>(json);40        return data != null;41    }42 43    public void DeleteSave()44    {45        if (File.Exists(SavePath))46        {47            File.Delete(SavePath);48        }49    }50}

Create an empty GameObject named SaveManager and attach this script.

Step 4: Capture Player Data

Create PlayerSaveAdapter.cs.

1using UnityEngine;2 3public class PlayerSaveAdapter : MonoBehaviour4{5    [SerializeField] private Health health;6 7    private string currentCheckpointId = "start";8 9    public PlayerSaveData Capture()10    {11        return new PlayerSaveData12        {13            x = transform.position.x,14            y = transform.position.y,15            health = health.CurrentHealth,16            checkpointId = currentCheckpointId17        };18    }19 20    public void Restore(PlayerSaveData data)21    {22        transform.position = new Vector3(data.x, data.y, transform.position.z);23        currentCheckpointId = data.checkpointId;24 25        // Add SetCurrentHealth to your Health component or restore through a proper method.26        Debug.Log($"Restore health to {data.health}");27    }28 29    public void SetCheckpoint(string checkpointId)30    {31        currentCheckpointId = checkpointId;32    }33}

Attach it to the Player and assign the Health component.

If your Health component does not support setting health yet, add a controlled method:

1public void SetHealth(int value)2{3    CurrentHealth = Mathf.Clamp(value, 0, maxHealth);4    HealthChanged?.Invoke(CurrentHealth, maxHealth);5}

Then call health.SetHealth(data.health) inside Restore.

Step 5: Create Checkpoints

Create Checkpoint.cs.

1using UnityEngine;2 3public class Checkpoint : MonoBehaviour4{5    [SerializeField] private string checkpointId;6 7    private void OnTriggerEnter2D(Collider2D other)8    {9        PlayerSaveAdapter saveAdapter = other.GetComponent<PlayerSaveAdapter>();10        if (saveAdapter == null) return;11 12        saveAdapter.SetCheckpoint(checkpointId);13        Debug.Log($"Checkpoint reached: {checkpointId}");14    }15}

Create a trigger object in your scene and attach this script.

Set:

• Checkpoint Id: forest_gate
• Collider2D: trigger enabled

When the player touches it, the checkpoint id changes.

Step 6: Save From a Game Controller

Create GameSaveController.cs.

1using UnityEngine;2 3public class GameSaveController : MonoBehaviour4{5    [SerializeField] private PlayerSaveAdapter player;6    [SerializeField] private SimpleInventorySaveAdapter inventory;7 8    private void Update()9    {10        if (Input.GetKeyDown(KeyCode.F5))11        {12            SaveGame();13        }14 15        if (Input.GetKeyDown(KeyCode.F9))16        {17            LoadGame();18        }19    }20 21    public void SaveGame()22    {23        SaveData data = new SaveData24        {25            player = player.Capture(),26            inventoryItemIds = inventory.CaptureItemIds()27        };28 29        SaveManager.Instance.Save(data);30    }31 32    public void LoadGame()33    {34        if (!SaveManager.Instance.TryLoad(out SaveData data))35        {36            Debug.Log("No save file found.");37            return;38        }39 40        player.Restore(data.player);41        inventory.RestoreItemIds(data.inventoryItemIds);42    }43}

This references an inventory adapter. If you do not have inventory yet, remove those lines for now.

Step 7: Save a Simple Inventory

If your inventory stores item definitions, save item ids instead of objects.

Create SimpleInventorySaveAdapter.cs.

1using System.Collections.Generic;2using UnityEngine;3 4public class SimpleInventorySaveAdapter : MonoBehaviour5{6    [SerializeField] private PlayerInventorySlots inventory;7    [SerializeField] private ItemDatabase itemDatabase;8 9    public List<string> CaptureItemIds()10    {11        List<string> ids = new List<string>();12 13        foreach (InventorySlot slot in inventory.Slots)14        {15            if (slot.IsEmpty) continue;16 17            for (int i = 0; i < slot.quantity; i++)18            {19                ids.Add(slot.item.itemId);20            }21        }22 23        return ids;24    }25 26    public void RestoreItemIds(List<string> ids)27    {28        // Clear inventory first. Add a ClearAll method to your inventory.29        foreach (string id in ids)30        {31            ItemDefinition item = itemDatabase.GetById(id);32            inventory.TryAdd(item, 1);33        }34    }35}

Create ItemDatabase.cs.

1using System.Collections.Generic;2using UnityEngine;3 4[CreateAssetMenu(menuName = "Game/Item Database")]5public class ItemDatabase : ScriptableObject6{7    [SerializeField] private List<ItemDefinition> items;8 9    public ItemDefinition GetById(string id)10    {11        return items.Find(item => item.itemId == id);12    }13}

This is simple, but it teaches the correct habit: save ids, then look up definitions when loading.

Step 8: Test the Save File

Press Play and test:

1. Move the player somewhere.
2. Pick up an item.
3. Touch a checkpoint.
4. Press F5.
5. Move somewhere else.
6. Press F9.

The player should return to the saved position.

On your computer, the save file is stored in:

1Application.persistentDataPath

Log this path if you want to inspect the JSON.

Step 9: Add Versioning Early

Your save format will change. Add a version now, even if it feels unnecessary.

Later, you can migrate old saves:

1if (data.version == 1)2{3    // Convert old fields into the new shape.4    data.version = 2;5}

Step 10: Common Mistakes

• Do not save passwords, tokens, or private user data in plain JSON.
• Do not assume save files are valid. Players can edit them.
• Do not save scene object references.
• Do not load before the scene has created the player.
• Do not forget to test loading an old save after changing your data classes.

Where To Go Next

Useful upgrades:

• Add autosave at checkpoints.
• Add multiple save slots.
• Add screenshot thumbnails for save slots.
• Add save migrations.
• Add encryption only if your game truly needs it.

The main lesson: saving is not magic. Capture plain data, write it to disk, then restore the game from that data in a controlled way.