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Unity Project Guide: Save and Load a Checkpoint With JSON - Game Development Guide | Checkpoint Zero

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:

TEXT
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.

CSHARP
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.

CSHARP
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.

CSHARP
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:

CSHARP
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.

CSHARP
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.

CSHARP
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.

CSHARP
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.

CSHARP
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:

Move the player somewhere.
Pick up an item.
Touch a checkpoint.
Press F5.
Move somewhere else.
Press F9.

The player should return to the saved position.

On your computer, the save file is stored in:

CSHARP
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:

CSHARP
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.

Unity Project Guide: Save and Load a Checkpoint With JSON

Unity Project Guide: Save and Load a Checkpoint With JSON

Step 1: Decide What Should Be Saved

Step 2: Create Save Data Classes

Step 3: Create the Save Manager

Step 4: Capture Player Data

Step 5: Create Checkpoints

Step 6: Save From a Game Controller

Step 7: Save a Simple Inventory

Step 8: Test the Save File

Step 9: Add Versioning Early

Step 10: Common Mistakes

Where To Go Next

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