Extensions

Every download, checked.

Extensions run at two moments in a download's life: before it starts, when they can hold it until you decide, and after it finishes. Their results show in each download's Checks tab.

OrbTorrent's Extensions page: a switch for all extensions, the Fake Download Check before a download starts and VirusTotal Scan after it finishes, and the official extensions with their switches

Before it starts
As soon as its files are known
Before any of a download arrives. A check that fails holds it, and the button reads Download Anyway, so nothing reaches your Mac until you choose.
After it finishes
When it's all on your Mac
Scan its files, tidy them away, or send yourself a notification. Each check's result shows with the download.

Official

Two to start with.

On from the start

Fake Download Check

Looks at the names and sizes of a download's files, before any of it arrives, for the signs fakes share. Everything happens on your Mac.

Runs: Before it starts
Looks at: File names and sizes
Sends: Nothing, anywhere

It holds

A program disguised as a video
A film with a program or installer in it
A video locked in an archive, with a password file

It warns about

A film far too small for its quality
Video only in .wmv
Links to download it elsewhere
A film with no video in it

With a free key

VirusTotal Scan

When a download finishes, it looks up each file's fingerprint on VirusTotal, which checks it against about 70 antivirus engines.

Runs: After it finishes
Fails: 3 or more engines call a file malicious
Warns: 1 or 2 do, since one-off false alarms are common
Uploads: Nothing, unless you turn that on

Checks programs first, then archives, then documents, and remembers answers for a week.
The free key allows 4 lookups a minute, so it waits between them.

Safe by design

Code from others, kept on a short leash.

OrbTorrent doesn't rely on reviewing extensions alone. It limits what their code can do.

A strict sandbox
Each run gets its own process that can't read files, reach the network or even look up a host name by itself.
Only what it lists
Every request goes through OrbTorrent, which checks it against the sites and files the extension listed when you installed it.
Time and memory limits
A check gets 15 seconds before a download starts, and 512 MB of memory. Go over, and it's stopped.
Passwords in the Keychain
An extension's passwords and keys go in your Mac's Keychain, and it only sees its own settings.
You see it first
Installing shows what an extension does and what it can reach, and asks before anything runs.
One switch
Turn every extension off to use OrbTorrent as a plain torrent client. Their settings wait for you.

Build your own

In TypeScript, or in a sentence.

Start one with a single command. It comes with tests that run without OrbTorrent, and loads into it as you save.

$ npm create @orbtorrent/extension@latest size-guard
$ npm test
$ npm run dev

Or describe what you want: on the Develop tab of OrbTorrent's Extensions page, it becomes a request for a coding agent such as Claude Code, Codex, Cursor or Gemini CLI, which writes it, tests it and tries it on your downloads. Nothing runs until you allow it.

Read the docs @orbtorrent/api on npm

src/check.ts

import { Download, Result, getPreferenceValues } from "@orbtorrent/api";

const gigabyte = 1_000_000_000;

/** Runs when a download's files are known, before any of it downloads. */
export default async function check(download: Download): Promise<Result> {
  const { limit } = getPreferenceValues();
  const size = (download.size / gigabyte).toFixed(1);
  if (download.size > Number(limit) * gigabyte) {
    // "failed" holds the download until you start it.
    return { status: "failed", summary: `It's ${size} GB, over your limit` };
  }
  return { status: "passed", summary: `${size} GB, within your limit` };
}

Share it as an .orbext file: opening one shows what it does and what it can reach, and installs it when you confirm. The SDK is MIT licensed, so your extension can use any licence.