OverviewHistoryStatsSecurity
npx skills add ...
Documentation
SKILL.md
npx skills add gamedev-skills/awesome-gamedev-agent-skills --skill save-systems
Design save/load for game state — choosing what to serialize, file formats, save slots, atomic crash-safe writes, schema versioning and migration, and autosave. Engine-neutral. Use when the user mentions save system, save/load, game state persistence, save slots, autosave, save file corruption, or migrating old saves to a new version.
npx skills add gamedev-skills/awesome-gamedev-agent-skills --skill save-systems
A save file is a serialized snapshot of game state that survives restarts. The hard parts aren't writing bytes — they're choosing what to save, writing it so a crash mid-save can't corrupt it, and reading old saves after you ship a patch. Get those three right and the rest is plumbing.
When not to use: for Roblox cloud persistence specifics, use
roblox-datastores. For the data model the save serializes (resources/SOs), use
godot-resources / unity-scriptableobjects. For Godot's FileAccess/
ResourceSaver and user:// paths, defer to the Godot engine skill while
applying the patterns here.
version integer. This is
the single most important field for a game you intend to patch.Rename-over-target is atomic on POSIX (same volume); on Windows a replace-by-rename
isn't guaranteed atomic, so keep the previous file as path + ".bak" before the
rename — that backup is what actually guarantees you can recover from a bad write.
version from version 1..bak.roblox-datastores).references/versioning-and-migration.md — schema evolution strategies, the
migration chain, backups/rollback, format trade-offs (JSON vs binary), and a
load-time validation checklist.roblox-datastores — cloud persistence, request limits, session locking.godot-resources, unity-scriptableobjects — the data model you serialize.procedural-gen — store the seed to regenerate worlds instead of saving them.rpg, survival-crafting, visual-novel — genres that compose this skill.# RIGHT: write to a temp file, then atomically rename over the target.
func save_atomic(path: String, data: Dictionary) -> void:
var tmp := path + ".tmp"
var f := FileAccess.open(tmp, FileAccess.WRITE)
f.store_string(JSON.stringify(data))
f.flush() # ensure bytes hit disk
f.close()
DirAccess.rename_absolute(tmp, path) # replaces the target; atomic on POSIX
# WRONG: opening `path` directly and writing in place — a crash mid-write leaves a
# truncated, unloadable save and destroys the player's progress.SAVE_VERSION = 3
def load_save(raw_bytes):
data = parse(raw_bytes) # JSON/binary -> dict
v = data.get("version", 0)
if v > SAVE_VERSION:
raise NewerSaveError(v) # save is from a newer build; refuse
while v < SAVE_VERSION: # apply migrations in order, v -> v+1
data = MIGRATIONS[v](data)
v += 1
data["version"] = v
validate(data) # check required keys / ranges
return data
# Each migration is a pure function from one version's shape to the next.
def migrate_1_to_2(d):
d["flags"] = {k: True for k in d.pop("completed_quests", [])} # list -> set-map
return d
MIGRATIONS = {1: migrate_1_to_2, 2: migrate_2_to_3}const SLOT_PATH := "user://save_%d.json" # manual slots 0..N
const AUTOSAVE_PATH := "user://autosave.json" # separate file: never clobbers a slot
var _autosave_cooldown := 0.0
func autosave_if_due(dt: float) -> void:
_autosave_cooldown -= dt
if _autosave_cooldown <= 0.0:
save_atomic(AUTOSAVE_PATH, capture_state())
_autosave_cooldown = 60.0 # throttle: at most once a minute
# Trigger an immediate autosave on checkpoints/level transitions, not mid-combat.