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Introduction

Welcome to VelumX — the Relayer-as-a-Service (RaaS) infrastructure for gasless transactions on the Stacks blockchain.

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The Problem

Traditional blockchain applications require users to hold native tokens (STX on Stacks) to pay for transaction fees. This creates real friction:
  • Onboarding barrier: New users must acquire STX before they can do anything.
  • Poor UX: Users manage multiple token types just to execute simple actions.
  • Adoption blocker: Limits DeFi growth by requiring upfront capital in the wrong asset.

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The VelumX Solution

VelumX is a Relayer-as-a-Service platform. Developers integrate gasless transactions by calling velumx.sponsor(txHex) — VelumX handles all the relayer infrastructure behind that single call.

Stacks-Native

Uses Stacks’ built-in sponsored transaction capability. No smart wallets, no account abstraction.

Multi-Tenant

Every developer gets an isolated relayer address and API key. Funds never mix.

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What VelumX Provides

ComponentDescription
Relayer BackendMulti-tenant key derivation, STX sponsorship, nonce management, broadcast
@velumx/sdksponsor(), estimateFee(), buildSponsoredContractCall()
DashboardAPI key management, relayer funding, usage stats, key export
Pricing OracleReal-time token→STX pricing for accurate fee estimation

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What Developers Provide

  • Their own contract calls (swap, bridge, stake — anything on Stacks)
  • Optionally: their own paymaster contract for USER_PAYS fee collection
  • An API key from the VelumX Dashboard

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Two Integration Paths

DEVELOPER_SPONSORS — simplest path. The developer’s relayer pays STX gas. Users pay nothing. 
// Build any Stacks contract call as sponsored
const tx = await buildSponsoredContractCall({ ... });
const signed = await wallet.sign(tx);
const { txid } = await velumx.sponsor(signed);
USER_PAYS — user pays a SIP-010 token fee. Developer deploys their own paymaster contract that atomically collects the fee and executes the action. 
// User pays fee in USDCx, action executes atomically
const tx = await buildSponsoredContractCall({
  contractAddress: 'SP...my-paymaster',
  functionName: 'swap-with-fee',
  functionArgs: [...]
});
const signed = await wallet.sign(tx);
const { txid } = await velumx.sponsor(signed);