GasPass

｜GasPass — An ERC-3525-based stored-value “gas card” that automatically or manually refuels gas across multiple EVM chains.

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Table of Contents

• Overview
• Architecture
• Features
• Smart Contract
• Tech Stack
• Integration SDK
• Use Cases
• License

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Overview

Category Description Type ERC-3525 Semi-Fungible Token (SFT) Purpose A stored-value gas card for multi-chain gas refueling Core Concept Users deposit USDC into an ERC-3525 slot; Vincent Agent automates gas top-ups when balances drop below threshold Key Technologies Lit Protocol, Avail XCS, Bungee Bridge API, Alchemy Gas Manager, EIP-712 Status Cross-chain prototype deployed on Arbitrum & Base testnets

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Architecture

[How It Works]

1. User Deposit Users mint a GasPass card and deposit USDC into the ERC-3525 GasPass Contract via MintWithSig. The deposited balance is locked inside the contract for future refueling operations.

2. Threshold Monitoring A Backend Monitor periodically checks the native gas balance of each target-chain wallet. When the balance falls below a defined threshold, it triggers a refill task.

3. Auto Mode (Vincent Agent) The Vincent Agent (Lit PKP) autonomously calls autoRefill() on the GasPass contract. It uses the stored USDC to create a cross-chain refill request, which is executed through Bungee to bridge and convert stablecoins into native gas.

4. Manual Mode

• Contract-Based: The Vincent Agent can initiate manualRefill() from the backend. This function still interacts with the GasPass contract, using deposited USDC to execute a one-time cross-chain transfer (through Bungee).

• Direct via Avail Nexus SDK: Alternatively, users can directly bridge funds using Avail Nexus SDK, performing a one-time cross-chain gas transfer from their own wallet.

5. Gas Top-Up On the destination chain, bridged stablecoins are swapped into native gas and credited to the Target Wallet.

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Features

Feature	Description
ERC-3525 Gas Slot	Each slot acts as a semi-fungible “gas wallet” holding USDC/USDT for a specific chain.
Permit-Based Minting	Supports EIP-712 + ERC-20 Permit2 signatures for gasless onboarding.
Vincent Agent (PKP)	Automated delegated execution powered by Lit Protocol’s Vincent Abilities.
Cross-Chain Refuel	Uses Avail’s Bridge & Execute and Bungee API for intent-based stablecoin transfers.
Alchemy Gas Manager	Sponsors or triggers gas top-ups via paymaster API.
Unified Slot Balance	Slot states and refuel logs recorded on Avail for verifiable auditing.

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Smart Contract

Contract: GasPass.sol Standards: ERC-3525 + EIP-712

Key Components

Module	Functionality
MintWithSig	Mints a new ERC-3525 token with user signature (EIP-712).
DepositWithSig	Deposits USDC/USDT via Permit2 authorization.
SetRefuelPolicy	Defines threshold, chain target, and trigger conditions.
ExecuteRefuel	Called by Vincent Agent once the policy condition is met.
UpdateSlotBalance	Updates slot’s on-chain value and Avail audit log.

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Tech Stack

Layer	Tools & Frameworks
Smart Contracts	Solidity, Foundry, OpenZeppelin, Solv ERC-3525
Cross-Chain Layer	Avail XCS, Bungee Bridge API
Automation Layer	Lit Protocol Vincent Abilities (PKP Agent)
Frontend	Vue 3, Vite, Vuetify, Pinia, Viem, Ethers.js
Backend / Infra	Node.js, Express, Alchemy SDK, Avail SDK

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Integration SDK

How GasPass Integrates with Vincent Agent

This sequence diagram illustrates how GasPass, Vincent Agent, and Bungee Bridge collaborate to perform secure, automated cross-chain gas refueling.

[Process Overview]

1. Monitoring Loop

The Monitor Service continuously checks each user’s target-chain gas balance according to their on-chain RefuelPolicy[tokenId][chainId].
This is an off-chain observation only — it cannot move funds or call contracts.

2. Trigger Condition

Once the wallet’s gas balance drops below the threshold, the monitor sends a signal to the Vincent Agent indicating that a refuel task is needed.

3. Delegated Execution

The Vincent Agent (Lit PKP), operating under a user-authorized Ability, directly calls: autoRefuel(tokenId, inbox, req, expectedSorHash, targetChainId)on the GasPass (ERC-3525) contract.
The Agent cannot act outside this Ability’s scope — it’s cryptographically constrained by user authorization.

4. On-Chain Enforcement

Inside GasPass, the contract:

• Verifies the executor’s PKP address is in the authorized list.
• Approves only the required amount of USDC for the Bungee Inbox.
• Creates a cross-chain refuel request with strict limits (spend cap, nonce, and expiry).

5. Cross-Chain Execution via Bungee

The Bungee Inbox forwards the request to the Bungee Gateway, which bridges and swaps stablecoins into native gas.
The Destination Wallet receives the gas directly, completing the automated top-up.

[Why Vincent]

In GasPass, all deposited USDC remains locked inside the ERC-3525 contract rather than in the user’s wallet.
An external “wake-up” is still needed to execute autoRefuel() when thresholds are breached.

To maintain security, the backend only signals that a refuel task is needed — it cannot execute it directly.
All actual fund movement or contract interaction is performed only through a Vincent Agent (Lit PKP) acting within user-authorized Abilities — predefined, cryptographically signed execution permissions that precisely define what functions the agent can call and under what conditions.

The contract recognizes the PKP’s address as an authorized executor only for those whitelisted Abilities.
Even if the backend or the Vincent service is compromised, any out-of-scope call would fail due to on-chain policy and signature verification.

[ability-sponsor-transaction]

To achieve a fully gasless user experience, we developed a custom package — ability-sponsor-transaction — inspired by the official Vincent SDK. This package extends the Vincent SDK’s design pattern but adds full Alchemy Gas Manager integration to support sponsored execution for arbitrary contract calls such as autoRefuel() and manualRefuel().

In the standard Vincent SDK, only a few built-in operations (like approve()) could be sponsored. However, the GasPass workflow required Vincent Agents to perform more complex on-chain calls, which also needed gas. To solve this, we studied the Vincent SDK internals and built our own ability-sponsor-transaction module — a drop-in extension that signs, wraps, and relays transactions through Alchemy’s Gas Manager API.

This module ensures that Vincent Agents can execute authorized contract functions without holding native tokens, while preserving the same cryptographic constraints and Ability-based authorization model defined by the Lit Protocol.

More detail in vincent-sponsor-transaction

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How GasPass Integrates with Avail

[Process Overview]

1. User selects “Avail Manual Refill” From the GasPass frontend, the user chooses Use Avail for Manual Refill and specifies

2. Generate Avail Intent The frontend builds a verifiable cross-chain intent using nexus-core / nexus-widgets: Includes guardrails such as minOut, maxSlippage, deadline, gasCeiling. The intent is encapsulated and signed as a cryptographic hash.

3. Wallet Sign & Submit The user’s wallet signs and submits the intent to the Avail Network. Avail automatically selects the optimal route and executes Bridge & Execute.

4. Cross-Chain Execution & Gas Top-Up Through its built-in Nexus Router + XCS Layer, Avail performs the bridge and swap, then credits the converted native gas to the target-chain wallet.

5. Status Tracking Each intent has a unique Intent ID. The GasPass frontend can query the execution progress, status, and final result via the SDK.

[Why Avail]

In GasPass, Avail is the only SDK that satisfies all three critical requirements for manual refueling: cross-chain execution, verifiable intent, and an open, chain-agnostic interface.

1. Supports “Bridge & Execute” Other bridge protocols (e.g., Bungee, Axelar) can only transfer assets, while Avail’s Bridge & Execute allows post-bridge execution in a single flow — for example, converting bridged USDC directly into native gas. This enables GasPass to offer a true one-click refill experience.

2. Intent-Based Verification Layer Avail’s Intent System transforms every cross-chain operation into a verifiable execution intent. Unlike traditional bridges that simply relay funds, each intent includes:

• Signature verification
• Execution guardrails (slippage, gas ceiling)
• Replay protection (nonce, expiry) These security primitives align perfectly with GasPass’s safety requirements.

3. Neutral and Open Execution Layer Avail is chain- and framework-agnostic, integrating seamlessly with the existing Vue + Node + ERC-3525 architecture of GasPass. It supports any destination chain — Arbitrum, Base, Polygon, Optimism, and more — allowing users to refuel from anywhere, to anywhere.

4. Complements the GasPass Automation Layer Vincent Agent and Avail play complementary roles in GasPass — two paths for cross-chain gas refueling.  Vincent Agent automates top-ups from USDC locked in the GasPass contract when wallet gas falls below a threshold.  Avail Nexus SDK enables manual, user-initiated refueling directly from the user’s wallet.  Together, they make GasPass both autonomous and flexible, supporting automatic and on-demand refueling. 

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Use Cases

• Hackathon Distribution: Distribute GasPass cards to participants, enabling them to instantly deploy smart contracts across multiple chains.

• Brand Marketing Giveaway: Companies can issue GasPass cards as raffle prizes to increase brand engagement and user loyalty.

• Onboarding Card for New Users: Web3 apps can gift GasPass cards to new users to lower the entry barrier and simplify their first on-chain experience.

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License

MIT License © 2025 GasPass Contributors