Middle/Senior Backend Engineer

ABOUT US

Xsolla is a global commerce company with robust tools and services to help developers solve the inherent challenges of the video game industry. From indie to AAA, companies partner with Xsolla to help them fund, distribute, market, and monetize their games. Grounded in the belief in the future of video games, Xsolla is resolute in the mission to bring opportunities together, and continually make new resources available to creators. Headquartered and incorporated in Los Angeles, California, Xsolla operates as the merchant of record and has helped over 1,500+ game developers to reach more players and grow their businesses around the world. With more paths to profits and ways to win, developers have all the things needed to enjoy the game.

For more information, visit xsolla.com.

ABOUT YOU

We are looking for a Middle/Senior Backend Engineer who is passionate about building scalable blockchain infrastructure and Web3 services to join our Xsolla ZK team. The best candidate will be someone who thrives in a fast-paced, highly collaborative, and exceptionally dynamic setting and is excited to develop backend systems that power NFT marketplaces, smart wallets, and blockchain-based gaming infrastructure.

Strong backend development skills in Go are essential, along with experience in building high-load distributed systems and working with databases. The ability to design resilient microservices architecture and integrate with blockchain networks will be key to your success in this role.

If you're passionate about building the infrastructure layer for next-generation gaming and love working on cutting-edge blockchain technology that enables gamers to truly own their digital assets, we would love to hear from you!

About the project

Xsolla ZK is building a cross-game infrastructure that empowers gamers to freely trade and use their digital assets without barriers. The backend team develops services for:

• Xsolla Bazaar - NFT marketplace for trading digital assets across Ethereum, Polygon, and Xsolla ZK chains

• Web3 Backpack - Smart wallet backend with account abstraction (ZK SSO 4337)

• Blockchain Services - Event scanners, transaction processors, and Web3 connectors

• BFF Layer - Backend-for-Frontend services orchestrating complex Web3 operations

Tech Stack:

• Language: Go (go-ethereum, ethkit, idiomatic concurrency patterns)

• Databases: MongoDB, PostgreSQL, Redis

• Message Queue: NATS, RabbitMQ, Kafka

• API: REST, WebSocket, gRPC, OpenAPI (Swagger)

• Blockchain Infrastructure:

• ZK Stack / ZKsync Era: EraVM, zksolc/zkvyper compilers, system contracts, bootloader, native Account Abstraction on zkSync-family chains

• Account Abstraction (ERC-4337): EntryPoint (v0.6-v0.8), UserOperation lifecycle (prepare→sign→submit→confirm), bundler and paymaster roles, ERC-7562 validation rules, ERC-6492 signature validation for undeployed accounts

• Ethereum L1: go-ethereum, abigen for smart contract bindings, RPC and indexer semantics

• Smart Contracts: Solidity, ERC-20/721/1155, modular account standards (ERC-7579 / ERC-6900), session keys (ERC-7710 / ERC-7715)

• Signature Schemes: EIP-712 typed data, ERC-1271 contract signatures, WebAuthn/passkey (P-256)

• Infrastructure: Docker, Kubernetes, GitLab CI/CD, Graylog

Key Technical Challenges:

• ZK Stack Integration: Working with EraVM execution environment, native Account Abstraction on zkSync-family chains, double resource accounting (EE gas + native computational resources), L1↔L2 communication via ZKsync Gateway, finality and reorg behavior

• Account Abstraction Backend Services: Implementing the ERC-4337 UserOperation lifecycle, integrating with bundlers and paymasters, handling gas estimation failure modes and counterfactual deployment

• Smart Contract Interaction: Generating Go bindings via abigen, handling factory dependencies for contract deployment, implementing EIP-712 transaction signing and ERC-1271 signature verification

• Session Keys & Delegated Permissions: Supporting scoped, time-limited, contract-allowlisted authority (ERC-7710 / ERC-7715) for gasless, prompt-free gameplay transactions

• Event Processing: Building blockchain event scanners for multiple chains (Ethereum, Polygon, Xsolla ZK), implementing reorg handling and transaction finality tracking

• High-Availability Architecture: Designing resilient microservices for NFT marketplace and wallet backends with real-time WebSocket updates

Responsibilities

• Develop backend services using Go with ethkit and go-ethereum for Ethereum interactions and RPC integration

• Integrate with ZK Stack infrastructure: work with EraVM, system contracts, and L1↔L2 messaging

• Build and maintain wallet backend indexing integrations for real-time token balance tracking and webhooks (via internal indexer or third-party providers)

• Design and implement APIs for NFT marketplace and orderbook services, including on-chain order matching and settlement flows

• Implement smart contract interaction layer using abigen-generated Go bindings for ERC-20/721/1155 tokens

• Build Account Abstraction (ERC-4337) backend support: UserOperation submission and monitoring, paymaster gas-sponsorship logic, session-key issuance and revocation

• Develop blockchain event scanners with reorg handling for Ethereum, Polygon, and Xsolla ZK chains

• Implement BFF (Backend-for-Frontend) services orchestrating complex multi-chain operations

• Design efficient caching and indexing strategies for on-chain data using Redis and MongoDB

• Write comprehensive tests including integration tests with local ZKsync test environment

• Document APIs using OpenAPI/Swagger specification

• Monitor and troubleshoot production systems, handle blockchain-specific edge cases (stuck transactions, gas estimation)

Nice to Have

Required:

• 2+ years of commercial experience with Go

• Strong understanding of MongoDB and PostgreSQL (query optimization, indexing)

• Experience with Redis for caching and session management

• Knowledge of message queues (NATS, RabbitMQ, or similar)

• Experience designing and implementing REST APIs with OpenAPI/Swagger

• Understanding of microservices architecture patterns

• Experience with Docker and container orchestration basics

• Proficiency with Git and GitLab CI/CD

• Solid understanding of distributed systems concepts

Preferred:

• Experience with Ethereum/EVM blockchain integration:

• Working with go-ethereum library and RPC nodes

• Smart contract interaction via ABI bindings (abigen)

• Understanding of transaction lifecycle, gas estimation, nonce management

• Knowledge of ZK Stack / ZKsync Era:

• EraVM execution model and differences from EVM, including native Account Abstraction on zkSync-family chains

• System contracts (ContractDeployer, NonceHolder, etc.)

• L1↔L2 communication, bridging, and finality/reorg behavior

• Working knowledge of ERC-4337 Account Abstraction:

• EntryPoint contract and the UserOperation lifecycle

• Bundler and paymaster roles, gas estimation failure modes

• Session keys and delegated permissions (ERC-7710 / ERC-7715)

• Familiarity with signature schemes: EIP-712 typed data, ERC-1271 contract signatures, WebAuthn/passkey signers

• Exposure to AA infrastructure providers (any of: Sequence, thirdweb, Privy, Dynamic, Turnkey, Pimlico, Alchemy, Biconomy, ZeroDev, Safe{Core}) for wallet, indexer, or transaction-relay integrations

• Knowledge of token standards (ERC-20, ERC-721, ERC-1155) and their implementation details

• Experience with blockchain event processing: event scanning, reorg handling, finality

• Understanding of DeFi concepts and NFT marketplace mechanics

• Experience with Kubernetes for container orchestration