The manifest

Every Pier mod is a directory under plugins/ holding a dynamic library and a manifest.json:

plugins/
  my-mod/
    my_mod.dll
    manifest.json

{
  "name": "my-mod",
  "entry": "my_mod.dll",
  "type": "pier",
  "version": "0.1.0",
  "description": "What this mod does.",
  "dependencies": [{ "name": "pier" }]
}

Fields

Field	Required	Notes
name	yes	Must match the directory name.
entry	yes	The library the build produced.
type	yes	Exactly pier.
version	yes	Semver.
description	no	Shown in /pier list.
dependencies	yes	Must include { "name": "pier" }.
reload_safe	no	true opens the mod to /pier reload. Default false.
load_level	no	Integer, default 0. Lower loads earlier.

The two that go wrong

type must be exactly pier. The host compares it literally against one string. Any other value and the mod is never scanned: no error, no log line, it is simply absent from /pier list. Pier's own CI has a check for this, because the failure reports nothing at all.

entry must match what the build produced. Cargo turns hyphens in a crate name into underscores, so the crate my-mod builds my_mod.dll. This is the easiest one to slip on.

Load order

Mods load in load_level order, lowest first, and mods sharing a level load by name. Omitting the field puts you at 0 with everyone else, which is where a mod with no preference belongs.

{ "load_level": -10 }

A level orders, it does not sequence. If your mod cannot work unless another one is already loaded, that is a dependency, and the host checks it and refuses to load you without it. A level only says which way to lean among mods that have a preference and nothing to hang it on: a permission manager that would rather register its gates before anything can consult them, say.

A non-integer value is reported as a problem in /pier list rather than treated as 0. Writing "load_level": "early" means an ordering was intended, and quietly giving that mod the default is exactly the silent fallback this project refuses elsewhere.

Dependencies

Listing pier is what orders the load, so that the host exists before your mod is dispatched to it. A name that is not pier is a dependency on a mod that does not exist.

Depending on another Pier mod works the same way:

"dependencies": [
  { "name": "pier" },
  { "name": "plot-manager" }
]

That orders the load. It does not make the other mod's API reachable; use a service or the bus for that.