Schedule One modding framework

S1API: cross-compatible Schedule One modding

Write one C# mod and ship it across Mono and IL2CPP builds with a stable API for NPCs, quests, items, phone apps, save data, world utilities, and runtime lifecycle hooks.

Install S1API Build your first mod Browse API reference

Get started

Choose the path that matches what you are doing.

Introduction

Learn what S1API solves and where it fits in the Schedule One modding stack.

Installation

Install S1API as a player, reference it as a developer, and understand the loader package.

Quickstart

Create a small mod, hook into lifecycle events, and move toward real content quickly.

Core concepts

Understand the runtime model before building larger mods.

Cross-compatibility

Use S1API abstractions instead of binding your mod directly to one Schedule One runtime.

Saveables

Persist mod state across save slots using S1API's save system and field annotations.

API modules

Jump straight into the gameplay systems most mods need.

NPCs

Create and manage custom characters, appearances, lifecycle hooks, schedules, dialogue, and runtime behavior.

Quests

Build quest lines, entries, markers, and completion logic around the game's quest flow.

Items

Register custom storable, additive, buildable, clothing, and equippable item definitions.

Products

Work with products, properties, packaging, additives, and product population helpers.

Phone apps

Add in-game phone applications, icons, screens, and phone-call driven interactions.

Law enforcement

Use checkpoint, curfew, patrol, pursuit, and dispatch abstractions for police-oriented mods.

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