Prerequisites: underneath everything below is a plain REST API (JSON over HTTPS), so any language works, and you can run an app yourself — self-hosted, on your own machine or server — without ever touching the Marketplace. The example apps on the Downloads list are Node.js scripts written this way — Node.js 18+ (for the built-in fetch) is the only thing you need installed to run or adapt them. If you've just installed Node.js and a command like node --version still says it's not recognized, open a new terminal window — Windows in particular won't pick up a PATH change in a window that was already open.

If you want to list on the Marketplace instead, what a buyer's install actually downloads depends on your app's runtime: a browser_sandboxed app is one code file, submitted as a .zip with its scryboard.json — no git clone needed, and there's a ready-to-submit starter template on the Downloads list at the top of the App API docs page. A node_cli app — anything calling an outside API, using a package, or needing a secret — ships as a small .zip (your code plus a scryboard.json manifest) and runs through the Scryboard App Runner, a small desktop app, rather than the buyer's browser. See Choosing a runtime below and the manifest reference before you start writing code — the runtime you pick determines what you can build with.

Trying your app on your own campaign before (or without) publishing: upload it as a personal app. Sign in, open /agents, and under Your Own Apps click Upload your app (.zip). It gets the same automatic checks a Marketplace submission gets, but nobody reviews it and nobody else can see it. Then pick one of your campaigns under Connect to: and click Connect. A browser_sandboxed app then runs whenever you have that campaign's page open; a node_cli app offers Get Runner link, which hands its token to the App Runner. To try a change, click Replace code on the app and pick the new .zip. This is the test loop for browser_sandboxed apps, which can't run anywhere outside Scryboard.

Testing without touching production: there's currently no separate staging deployment of Scryboard — the only live environment is production. Rather than pointing a new app under development at your real campaign with a real token, use the mock server first: it's a zero-dependency local stand-in for this entire API, backed by fixture data, with a preview page so you can see your pushed widgets rendered without writing anything to a real database. Do one final pass against a real token before publishing, since the mock is a fixture and can drift from actual behavior over time.