Getting Started with OpenTTD Modding
In-game Online Content browser, NewGRFs, AI/GS scripts, and multiplayer
OpenTTD is one of the most accessibly-moddable games on this list because everything happens through the in-game Online Content browser. No third-party launcher, no asset extraction tools, no manual file management for typical content.
This guide walks the standard install on current OpenTTD.
Step 1 — Open the in-game Online Content browser
OpenTTD → Game Options → Online Content.
The browser shows content categories:
- NewGRFs — graphics replacements (locomotives, road vehicles, stations, terrain).
- AIs — competitor AI scripts (Squirrel-based).
- Game Scripts (GS) — global behaviour mods.
- Scenarios — pre-built starting situations.
- Heightmaps — custom map terrain.
- Base graphics / sounds / music — wholesale replacements of vanilla.
Download what you want; OpenTTD downloads into the right folders.
Step 2 — Apply NewGRFs to a new game
When starting a new game, the setup screen has a NewGRF Settings button. Add downloaded NewGRFs to the active list and configure their parameters.
NewGRFs are per-game: each save remembers which NewGRFs were active when it was created.
Step 3 — Pick AIs (optional)
Game setup → AI / Game Script Settings → add downloaded AIs to compete against you.
Each AI has its own play style. The community has built dozens of distinct competitors.
Step 4 — Game Scripts (optional)
GS scripts add global behaviour: dynamic missions, town-growth challenges, economic events. Configure in the same AI/Game Script Settings dialog.
Step 5 — Multiplayer
OpenTTD's multiplayer infrastructure is mature. Joining a server auto-syncs NewGRFs from a server-side mirror if needed.
Step 6 — Author your own
OpenTTD's source is fully open. NewGRF authoring uses the NML language (compiled from NewGRF Meta Language to the binary NewGRF format). AI/GS authoring is Squirrel.
Tutorials live on the OpenTTD wiki.
Common gotchas
- NewGRF added mid-save. Some NewGRFs can be added/removed mid-save; some can't. The save's NewGRF list shows which.
- Mod incompatibility. Two NewGRFs replacing the same vehicle class can produce visual conflicts. Order them carefully.
- AI behaviour seems wrong. AI scripts are pure community work; quality varies.
- Online Content unreachable. Check that bananas.openttd.org is accessible. The browser uses the same content pipeline.
OpenTTD is one of the rare games where "modding" is genuinely as native as base play. Worth recommending to anyone interested in how a fully open-source game handles community content.