Play well with other mods

A player may run your mod alongside several others. None of them coordinate directly with each other — plan for that instead of assuming your mod is alone in the process.

Hooks: expect to lose the race sometimes

Every mod, and a few of T3SDK's own built-in fixes, share one hook table (see Hook a game function). CreateHook fails with MH_ERROR_ALREADY_CREATED when the address is already taken, by another mod or by T3SDK itself. There is no way to ask who holds it, or to reserve it in advance:

int status = api->CreateHook(target, reinterpret_cast<void*>(&Detour), reinterpret_cast<void**>(&original));
if (status != 0) {
    api->Log("could not hook the target (MH_STATUS %d); continuing without it", status);
    // fall back, or return 1 from T3Mod_Init if the feature is essential
}

Decide, per hook, whether losing it is something your mod can work around (log it and skip the feature) or a reason to refuse to load outright (return non-zero from T3Mod_Init, after removing any hook you already created — see The mod lifecycle).

Load order decides who goes first

Packaged mods run in the launcher's order (load-order.txt), then loose DLLs by file name. Load order decides:

• which mod's T3Mod_Init runs first, and so which one wins a contested hook;
• which mod's files//textures/ file wins when two provide the same path (later wins).

Declare requires and conflicts in mod.json so the launcher can order and check your mod correctly, instead of hoping players get it right by hand; see Packaging and Mod packages.

Check the API version, not just your own build

Set mod.json's api to the lowest T3SDK_API_VERSION your mod actually needs, and guard any call added after version 1 with the size check in The mod lifecycle. A player with an older T3SDK than the headers you built against should only see a warning if your mod truly cannot run without a newer call.

Don't assume you are the only mod touching the engine

Frame and log callbacks from every loaded mod, and the game itself, share the same engine state. T3SDK isolates callback crashes — one mod's faulting callback does not stop another's (see Debug a mod) — but it does not isolate their effects: if your hook changes something another mod or the game reads, that change is visible everywhere. Prefer calling through to original unless replacing the call outright is the point, and keep a hooked function's contract (its return value, what it writes through its pointers) intact for whoever else calls it — including T3SDK itself, for the few functions it calls directly (see Hook a game function).

There is no mod-to-mod API

T3SDK connects mods to the game, not to each other: as of API version 1 there is no call to find another mod or exchange data with it. If your mod genuinely depends on another one's features, say so with requires in mod.json so the launcher enforces the order and presence, and have that other mod expose whatever it offers itself — its own exported functions, its own file format, and so on. T3SDK neither helps nor prevents that, and it is untested here.

Reference

• Hook a game function, The mod lifecycle, Packaging, Mod packages.