Senior Software Development Engineer In Test / SDET / Quality Lead

io.tt is growing quickly, and we are investing in quality as a core part of how we build. We are looking for a hands-on Senior SDET / Quality Lead to own our testing strategy and automation as the platform scales. This is a foundational role: you will shape how quality engineering works at io.tt and build the automated frameworks that let our teams ship quickly and with confidence.

Our engineering and product teams move fast and lean, making strong use of modern, AI-assisted tooling. You will bring the strategy and engineering depth that lets us keep raising the bar as we grow: deciding where to focus testing effort, building robust automated coverage, and making sure the insights and analytics we deliver to enterprise brands are accurate and dependable.

Our customers are global enterprise brands, so reliability and trust matter enormously. Keeping a rich, evolving platform dependable at scale calls for judgement and technique: risk analysis, contract and property-based testing, backward-compatibility assurance, data validation and visual regression. You will work closely with product, design and engineering, and you will be as comfortable defining a quality bar as writing the code to enforce it.

This role reports to the Head of Engineering and is based in our central London (EC1V) office, hybrid with 2 days on-site per week. We offer 20 days holiday plus a festive shutdown, with an additional day per year of service (capped at 5), private medical insurance with Vitality after probation, a company pension and sick pay, a cycle to work scheme, and "Work From Anywhere" for one week a year (UK time). The office is dog-friendly and stocked with breakfast, drinks and snacks, with regular team events and a casual dress code.

What you'll do

• Owning test strategy across the platform: defining what quality means for io.tt, where the real risk sits, and how we prove it before customers do.
• Building and maintaining the end-to-end and integration test safety net (e.g. Playwright) with CI gating, focusing on the cross-service coverage that unit tests miss.
• Ensuring backward compatibility, so that experiences customers have already published continue to render and behave correctly as the platform's features and schema evolve.
• Testing a configuration-driven product by applying contract, model-based and property-based testing across the wide range of experiences customers can create.
• Validating analytics and data correctness, verifying pipeline integrity and aggregation accuracy across our Postgres and MongoDB data layers. Wrong numbers erode enterprise trust quietly and permanently.
• Owning visual-regression and cross-browser and cross-device testing on the experiences customers publish, protecting the brands that depend on us.
• Building accessibility (WCAG) checks into the test strategy, in line with enterprise and brand requirements.
• Curating and improving the AI-generated tests the team produces, raising their quality and closing gaps in coverage.
• Acting as a consistent voice for quality across product, design and engineering, and helping the team ship faster with confidence.

What we're looking for

• Strong hands-on engineering ability in TypeScript. You live in the codebase and write test infrastructure as production-quality code.
• A systems-and-risk mindset, focused on what could break and what matters most rather than on test counts.
• Depth in at least one of: testing configuration-driven or composable systems (contract, model-based or property-based testing), or data-pipeline and analytics validation. Both is a strong plus.
• Experience designing and building automated E2E, integration and visual-regression frameworks and wiring them into CI/CD.
• Comfort working alongside AI-assisted development, using tools like Claude to accelerate test creation, then vetting and hardening the output.
• The ability to take an ambiguous product and turn it into a clear, prioritised quality strategy.
• Strong communication skills, and the confidence to set and hold a quality bar across teams.
• 6+ years in software quality and test engineering, including senior or lead-level ownership of test strategy.
• Proven experience building automated test frameworks for a SaaS product (ideally web-based and complex).
• Hands-on TypeScript, and comfort in a Node or Bun back-end environment with relational and document databases (Postgres and MongoDB).
• Experience working closely with engineering, product and design teams to embed quality into delivery.
• Exposure to CMS, analytics or other configuration-heavy SaaS platforms is a strong advantage.