What you know

You have the overall architecture, but not enough detail to build a production-ready plugin system from scratch. Think of it this way:

✅ You understand the concept.
✅ You understand why it works.
❌ You don’t yet have all the implementation details and design decisions.

Here are the pieces you already have.

What you know

You know that:

Plugins are separate executables.
Each plugin has a manifest (plugin.toml or similar).
The app discovers plugins by scanning a plugins directory.
The app launches plugins when needed.
Plugins communicate using a language-independent protocol (JSON over sockets, stdin/stdout, or HTTP).
Plugins can expose capabilities like search, stream, and download.
Plugins can be written in any language.

That is the core architecture.

What you’re still missing

To actually build it, you need to define the “contract” between your app and plugins.

1. The manifest format

For example:

id = "spotify"
name = "Spotify"
version = "1.0.0"
entry = "./spotify"

capabilities = [
  "search",
  "stream",
  "download"
]

You need to decide:

Required fields
Optional fields
Versioning
Dependencies
Permissions

2. The communication protocol

This is the most important part.

For example:

App
 ↓
{
  "id":1,
  "method":"search",
  "params":{
      "query":"Coldplay"
  }
}

↓

Plugin

↓

{
  "id":1,
  "result":{
      ...
  }
}

You must define:

Request format
Response format
Error format
Timeouts
IDs
Notifications/events

This becomes your API specification.

3. The data models

For example:

Track

Album

Artist

Playlist

SearchResult

Download

Stream

Every plugin must return the same structure.

Example:

{
  "id": "123",
  "title": "Believer",
  "artist": "Imagine Dragons",
  "duration": 204,
  "streamUrl": "...",
  "coverArt": "..."
}

If every plugin invents its own format, the system won’t work well.

4. Plugin lifecycle

You need to answer questions like:

When are plugins started?
Do they stay running?
Do they exit after one request?
Can multiple requests run simultaneously?
How are crashes handled?
How are updates installed?

5. Discovery

How does the app find plugins?

Example:

plugins/

    spotify/

        plugin.toml
        spotify.exe

    soundcloud/

        plugin.toml
        soundcloud

6. Permissions

Should every plugin be allowed to:

Access the internet?
Read local files?
Delete files?
Store data?
Execute other programs?

A permission system helps protect users.

7. SDK (optional)

Although plugins can be written in any language, you’ll probably want to provide helper libraries.

Example:

Python SDK

Go SDK

Rust SDK

Node SDK

They don’t replace the protocol—they just make it easier to implement correctly.

8. Error handling

Define standard errors.

For example:

PLUGIN_NOT_FOUND

AUTH_REQUIRED

SEARCH_FAILED

DOWNLOAD_FAILED

NETWORK_ERROR

RATE_LIMITED

Then every plugin reports errors consistently.

If I were designing this system today

I’d use a structure like this:

Music App
    │
Plugin Manager
    │
Manifest Loader
    │
Plugin Process Manager
    │
JSON-RPC Layer
    │
Capability Dispatcher
    │
Playback Engine

Each layer has a single responsibility, making the system easier to extend and maintain.

Do you have enough to build it?

You have enough to start designing and building a first version, especially if it’s for learning or a prototype.

For a polished, extensible system, you’ll need to write a plugin specification that defines:

The manifest schema.
The communication protocol.
The data models.
The lifecycle.
Security and permissions.
Version compatibility.

That specification becomes the contract every plugin follows, regardless of the programming language it’s written in.

Given the direction you’re describing, a complete plugin specification would likely be 30–80 pages of documentation. The actual implementation of the plugin manager might only be a few thousand lines of code, but the quality of the system depends far more on having a clear, stable specification than on the amount of code.