Playground

playground-tau-beige.vercel.app is a real, live instance of @lumenline/widget embedded on its own page, not a mockup, not a screen recording. It runs the exact <lumenline-widget> custom element described on the Widget page, against real Stellar testnet infrastructure, with a real protocol inspector alongside it that shows the actual XDR, attestation, and relayer traffic as it happens.

What it demonstrates

The playground is deliberately narrow, one real path, not a menu of every rail this project supports: outbound only, Stellar → Ethereum Sepolia, USDC via CCTP. That's the direction that exercises the most real machinery in one flow, per its own on-page copy: the two-step approve-then-burn sequence, the real prepareStep polling mechanism, and registerOutboundTransfer's relayer-registration path. USDT0 isn't offered here for the same structural reason it isn't offered anywhere on testnet, see Core Concepts.

Every quote, build, and signature is real: a real Circle Iris fees call, a real Soroban RPC submission, a real on-chain testnet transaction once you sign. The protocol inspector alongside the form captures this traffic passively, through the same window.fetch/console interception mechanism described in the playground's own source (apps/playground/lib/inspector-capture.ts), so what it shows you is the actual request/response, not a formatted-after-the-fact summary.

What you need to actually complete a transfer

The playground itself needs no setup, but signing a real transaction does, because this is real signing, not a simulated one:

• Your own Stellar testnet account and wallet extension. The widget connects to whichever wallet you pick and signs with whatever account that wallet currently holds, there's no shared "demo wallet" mode, and no check anywhere that lets you type one address into the "Sender" field while signing with a different connected account, see Wallet support for which wallets are actually confirmed to work end-to-end (Freighter, so far).
• That account funded on testnet. Two real, public faucets, no API key needed, linked directly on the page itself: Friendbot for XLM, Circle's testnet faucet for USDC.
• A destination address on Ethereum Sepolia to receive the USDC. It doesn't need to sign anything or hold any ETH for this flow, delivery gas is paid on the destination side (either by a configured relayer, or by whoever submits the attested message manually, see below), not by the recipient.

Automatic delivery, or manual, honestly

Whether a transfer completes delivery on Sepolia automatically depends on whether this specific deployment has a relayer configured, exactly the same real, disclosed distinction as the widget's own outbound registration behavior generally, not something this page can promise on the deployment's behalf. The playground surfaces which case you're in directly in its own UI, not left for you to guess:

• If no relayer is configured, or a configured one is unreachable or misconfigured, the widget says so plainly once your burn transaction lands, and receiveMessage remains genuinely permissionless by CCTP's own design, so the transfer isn't stuck. See the end-to-end walkthrough for the real manual-completion path.
• If a relayer is configured and reachable, the widget registers with it automatically once your burn confirms, and you can watch the real registration request and its response in the protocol inspector, not just trust a status label.

Source

The playground itself is real, open source code in this repo, apps/playground, built the same Next.js app either you or anyone else can run locally against your own relayer instead. See the "View source" link in the playground's own header, or GitHub directly.