Full-Stack Engineer (Security)

Relay; United Kingdom; Remote; GBP 120,000 - 160,000; Full time

Benefits offered by this job

Competitive base salary

Equity package

Comprehensive health benefits

Unlimited PTO policy with encouraged•

Remote-first culture with emphasis on

Job summary

Relay is hiring a full-stack engineer focused on security. You will own critical production security systems, write code daily, deploy to production, and partner with product engineers to ship secure features across wallets and MEV protections.

You will work with a security-minded team, contribute to audits and incident responses, and help scale defenses in a remote-first, fast-paced environment.

Qualifications

• Hands-on full-stack engineering with production deployment experience.
• 4+ years building and running production systems with security focus.
• Strong TypeScript skills across backend, databases, and small UIs.
• Experience with detection, screening, fraud, or abuse prevention systems.
• Ability to read Solidity and assess automated findings against contracts.
• Experience operating security tooling in a CI/CD workflow.
• Threat modelling and security reviews with product teams.
• Familiarity with secrets management and IAM/auditability.
• Excellent incident write-ups and postmortems.

Responsibilities

• Own wallet screening microservice end to end, including latency and uptime.
• Own sandwich-attack tracker and bring it to production with monitoring.
• Maintain Vigil auditing tool and ensure accurate findings triage.
• Build the detection and response loop with automated monitoring and alerts.
• Collaborate with product teams to ship secure-by-default features.
• Threat-model new features and review changes for security risk.
• Extend Vigil to support evolving threats and data flows.

Skills

Full-stack engineering

TypeScript

Security in production

Solidity basics

Kubernetes

Incident postmortems

MEV/blockchain security

Threat modelling

Crypto security

LLM tooling

Tools

Kubernetes

LLM tooling

Job description

About Us

Relay is a cross-chain payments protocol that provides instant, low-cost cross-chain bridging, swaps, and transactions. We're the fastest and cheapest way to bridge and transact across chains, serving over 5 million users who have completed 59+ million transactions with $6+ billion in volume across 85+ chains.

About Us

Relay is a cross-chain payments protocol that provides instant, low-cost cross-chain bridging, swaps, and transactions. We're the fastest and cheapest way to bridge and transact across chains, serving over 5 million users who have completed 59+ million transactions with $6+ billion in volume across 85+ chains.

Our mission is to make transacting across chains as fast, cheap, and reliable as online payments. We are building the core infrastructure to abstract chains from end user payments, enabling the next billion users to experience the benefits of blockchain without the UX burdens.

About The Role

We're hiring a full-stack engineer who cares deeply about security to work side by side with our Head of Security, who leads security at Relay. Money moves through our systems 24/7, and attackers, from address poisoners to MEV searchers, are watching the same flows we are. Your job is to make Relay a hard target and to make security something product teams can build in, not bolt on.

Development runs in containers. Production access is read-only by default, with a written path for state-changing actions. Decisions are recorded with their evidence and reviewed later. We lean on AI-assisted tooling, including our own audit agents, and expect you to extend it rather than start over.

In this role, you'll own several production security systems end to end, each of which is a detection or denial control, and you'll partner with product engineers to ship security features that users and integrators can see and trust. This is an individual contributor, hands-on full-stack engineering role. You'll write code every day, deploy it, and run it in production: building services and the tools and interfaces around them, instrumenting them, setting up monitoring and alerts, and being on call for what you ship.

What you'll do

Own our wallet screening microservice

• Own the service that screens wallet addresses before and during transactions: verdict quality, caching and rescreening behaviour, latency, and uptime
• Recommend and integrate risk vendors and data sources, and decide at which stage of a transaction (quote, deposit, fill, refund) and on which chains and address roles (sender, recipient, intermediary) each one applies
• Make blocking decisions explainable: clear error codes and messages for integrators, and auditable reports of what was blocked and why
• Build the override and watchlist tooling around the service with caller authorisation, confirmation steps, and an audit trail
• Handle partner and compliance requests about screening coverage, including blocked-address reporting
• Keep the fail-closed guarantees honest across every flow that moves funds, including refunds, and prove it with tests

Own our sandwich-attack tracker

• Turn the tracker into a production system that detects sandwich attacks and other MEV extraction against our users' transactions, in near real time
• Measure it: precision and recall against labelled cases, per chain, with the back-test suite in CI
• Quantify impact by chain, route, and integrator, and trace attacks back to where a transaction became visible
• Work with Solving, Infrastructure and Protocol engineers to design mitigations, such as private submission, routing changes, and slippage guidance, and measure whether they work
• Run investigations with our Head of Security when an incident is live and write up what happened and what changed

Maintain Vigil, our internal auditing tool

• Own Vigil as a product for our engineers: keep it reliable, keep its checks current, and decide what it audits next
• Treat it as what it is, an LLM-driven audit harness: prompt and rule changes are production changes, every false-positive rule carries evidence, and a regression set keeps it honest
• Keep findings triage accurate and actionable, with clear severity, ownership, and a path from finding to fix (including delegation to our internal AI agent and Linear tickets)
• Cut noise and false positives so teams trust Vigil's findings and act on them
• Extend Vigil as our systems and threats change, feed incidents back into it, and make sure its findings feed the screening service, the sandwich tracker, and product security work

Build the detection and response loop

• Run the daily loss review as an automated job with alerting, and own the monitors that catch mispricing, unexpected refunds, and fills that deviate from their quotes
• Build the watchlist and early-warning pipeline that denies exit rails to the proceeds of third-party hacks within the hour
• Write the postmortem, that pertain to your domain, and turn its lessons into a check, a monitor, or a rule

Build security features with product teams

• Sit with product teams at design time to threat-model new features, especially anything that moves, holds, or refunds funds
• Build shared security building blocks (permissions, caller-scoped reads with field allowlists, audit trails, secrets handling, rate and abuse controls) so teams reuse them instead of reinventing them
• Review changes for security risk and help teams adopt secure-by-default patterns
• Use AI-assisted tooling to review code, enumerate attack paths, and triage findings faster

About You

• You build the feedback loop for your own judgement: back-tests, regression sets and post-incident checks, because the misses that cost the most looked harmless at first
• You've run security-sensitive systems in production
• You enjoy working with product engineers and can turn a threat model into a change they're glad to make
• You're curious about crypto's adversarial conditions: MEV, mempools, address poisoning, sanctioned and illicit flows
• You're comfortable being on call for 24/7 financial infrastructure and calm during live incidents
• You write things down: a decision with its evidence, an incident with its timeline, a finding with its severity and owner

Skills And Abilities

Must-have

• Hands-on full-stack engineering experience: you build, deploy, and maintain production services yourself, including instrumentation, logging, monitoring, and alerting
• 4+ years as a software engineer building and running production systems, with a real interest in security (you don't need a security title)
• Strong TypeScript, and comfort across the stack: backend services, databases, and small internal UIs; you can also review other people's code for security flaws
• Distributed-systems correctness: queues, retries, idempotency, race conditions, and unit or decimal boundaries, and the habit of asking what happens when a response is lost or a job runs twice
• Experience building or operating detection, screening, fraud, or abuse-prevention systems, and measuring them against ground truth: precision, recall, and the cost of each kind of error
• On-chain transaction analysis on EVM chains: receipts, logs, block ordering, pool mechanics, and the tooling to trace funds and cluster wallets
• Experience operating LLM-based automation in production: evals, regression sets, and prompt or rule changes treated with the same discipline as code
• Containers and cluster deployment: you can land a service in a Kubernetes cluster with its secrets in the secret store, not on a personal account
• You can read Solidity well enough to judge whether an automated finding against a contract is real
• Experience threat modeling and running security reviews of new features with product teams
• Familiarity with secrets management, identity and access, auditability, and safe handling of side effects
• Strong written communication for incident write-ups and partner or compliance questions; you've written a postmortem that changed a system

Nice to have

• Experience with Rust (we use a little of it, and you'll read more than you write)
• Smart contract auditing, wallet security, or deeper MEV and mempool experience
• Experience with AML, sanctions, or wallet-risk vendors and the integrations around them
• Experience building indexers or block-level tooling
• Experience in payments, exchanges, or another high-stakes domain
• Applied offensive mindset: you've reproduced an exploit against your own systems, written a proof of concept from a vague report, or run purple-team exercises, and you can walk a finding from the data it exposes to what an attacker would actually do with it
• Awareness of security trends and industry-specific threats

What we offer

• Competitive base salary
• Equity package
• Comprehensive health benefits
• Unlimited PTO policy with encouraged minimum
• Remote-first culture with emphasis on collaboration, communication, and flexibility