Principal Software Engineer in London

Logistics: Hybrid - 1-2 days per week in our London HQ

Alto Software Group powers more than half of all UK housing transactions each year.

Estate and letting agents run their whole business on Alto, every day: winning instructions, marketing homes, agreeing sales, moving tenants in and managing properties for years after.

The platform behind that is large and proven, and we're investing in its next generation: moving it, one part at a time, onto a modern architecture while agents keep using it every day.

The new platform is built for people and AI agents alike: anything a person can do, an AI agent can do safely on their behalf, with the same permissions, data protection and audit trail as a person.

It's one of the hardest and most interesting engineering problems we have, and we want someone who'll love it.

The role in one line

You'll lead how Alto moves onto its next-generation platform: a platform ready for AI agents as much as for people.

You'll decide how it should work, build the foundations yourself, and create the blueprint for other teams to follow.

What that looks like day to day

You'll own the target architecture: the key design decisions, the boundaries between the parts of the system, and the standards everything else is built to.

You'll spend much of your time in the code, proving those decisions by building the platform and moving real features onto it.

Then you'll guide the teams who build on it, reviewing their designs and removing what slows them down.

Nothing here is fully decided.

We have an early direction and a working proof of concept, and we want you to challenge both.

Once a decision is yours, it's yours end to end: the design, the build, the roll-out to real customers, and the plan for when something goes wrong.

Day to day you'll work across

• . NET and Type

Script: .

NET for the core platform capabilities, where the business rules live once, and Type Script for the workflows and AI agents built on top of them, with React micro-frontends on the front end, all on AWS.

• Core business capabilities come first, in . NET: carved out of the existing monolith rather than rewritten, so there's one source of truth for business logic and nothing drifts.
• The Jobs of Work layer, the end-to-end workflows people and AI agents run, is built in Type Script on top of them.
• You'll be moving key production data to modern database services while it's in live use, and keeping every agency's data separate and safe the whole time.

AI agents are first-class users of what you build.

That means clear, well-described capabilities they can call, permissions they can't step around, actions that are safe to retry, a full record of what an agent did and for whom, and a human sign-off wherever money or legal steps are involved.

We build with AI, not around it. AI coding assistants are standard kit here.

Who you are

• You've moved a live system before. Old and new ran side by side for real customers, and you know what took the longest.
• You see through technical debt.

You understand the debt that comes with a long-lived codebase and business logic hidden deep in the data layer, and you lead how to displace it safely, keeping data correct while it moves.

• You've built for AI agents, or want to.

You understand what it takes for an agent to act safely in a real business system, and you design for it from the start rather than bolting it on.

• You think in boundaries. You can say who should own which data and why, and you turn those rules into code, not wiki pages.
• You set the technical strategy. You set a clear technical direction and get teams you don't manage to follow it, through clear written decisions, design reviews and pairing.
• You'd rather show than tell. You share a proof of concept with confidence, not a polished plan, because early feedback beats being right alone.
• You care about the people on the other end. A clever migration that disrupts an estate agent's day isn't a success.
• You communicate clearly, whether it's a design note, a trade-off explained to a product lead, or an update for the business.
• What success looks like in a year
• The first part of Alto runs on the new platform in production, for real agencies, with a tested way back.
• A second team has moved its part mostly on its own, using what you built.
• The new platform measurably improves performance and scale.
• AI agents are doing real work for agencies through the platform, with the same safeguards as people.
• Engineers across Alto know how the platform works and why.
• Everyday Flex - greater flexibility over where and when you work
• 25 days annual leave + extra days for years of service
• Day off for volunteering & Digital detox day
• Festive Closure - business closed for period between Christmas and New Year
• Cycle to work and electric car schemes
• Free Calm App membership
• Enhanced Parental leave
• Fertility Treatment Financial Support
• Group Income Protection and private medical insurance
• Gym on-site in London
• 7.5% pension contribution by the company
• Discretionary annual bonus up to 10% of base salary
• Talent referral bonus up to £5K

We want to make ASG more welcoming, fair and representative every day.

We'll consider everyone who applies for this role in the same way, regardless of your ethnicity, colour, national origin, religion, sexual orientation, gender, gender identity, age, physical disability, neurodiversity status, family or parental status, or how long you've spent unemployed.