Fractional CTO
London, UK
One advisory engagement open
AlexWilliams — Fractional CTO for pre-seed to Series A teams
AI made your engineers faster at writing code and slower at shipping it. I rebuild the review practice, the hiring bar and the delivery system around that.
Fractional CTO for pre-seed to Series A teams — one engagement at a time, alongside my own CTO job.
hello@alexwllms.com- In engineering, 6 leading it
- 13 yrs
- Insurtech valuation, employee 20
- $1.25bn
- Engineers interviewed in six months
- 50+
Services
Three ways to hire me
Two are fixed pieces of work; the third is the ongoing seat. Scope and price are in each.
AI Tooling & Delivery
Your team adopted AI and got faster at writing code. The bottleneck moved to reviewing it.
AI Tooling & Delivery
Your team adopted AI and got faster at writing code. The bottleneck moved to reviewing it.
Across the industry AI has lifted throughput by 2–18% while making delivery less stable. Median time in code review is up 441%, and 31% more pull requests now merge with no review at all. Teams feel faster at the keyboard and get slower as a delivery system, and the dashboards keep saying everything is fine.
I rolled AI tooling out across the engineering team at Propelr this year: which tools earn their licence, where they quietly make things worse, and what has to change in review, testing and release practice when a third of your code was not typed by a human. That is an engineering management problem rather than a model problem, which is exactly why handing it to an ML specialist does not fix it.
What you get
- An honest read on where AI is helping you and where it is costing you
- Review, testing and release practice rebuilt for AI-volume code
- Working sessions with the engineers who have to live with it
2–3 weeks · fixed fee from £9,000
Hiring When AI Writes the Code
Take-homes are dead and live coding is contaminated. You still have to tell good engineers from confident ones.
Hiring When AI Writes the Code
Take-homes are dead and live coding is contaminated. You still have to tell good engineers from confident ones.
Ninety per cent of developers now use AI tools and roughly 41% of committed code is AI-generated. Every signal your interview process was built on has been degraded, and most teams have quietly stopped trusting their own loop without ever saying so out loud.
The founders at Marshmallow picked me as the company’s Bar Raiser. I ran over fifty interviews in six months while engineering went from under ten people to over sixty, and then rebuilt the hiring process from scratch again at Vita Mojo. I redesign the loop for a world where the candidate has the same tools you do, and sit on it until your own senior people can hold the bar without me.
What you get
- An interview loop that still works when candidates use AI
- Scorecards, levelling, and a written bar your team actually agrees on
- Final-stage interviews run by me until your team can
Fixed scope · from £6,000
Fractional CTO
Technical leadership on a weekly cadence — the roadmap, the delivery and the board conversation.
Fractional CTO
Technical leadership on a weekly cadence — the roadmap, the delivery and the board conversation.
A ninety-minute leadership session in the diary every week, async access in between, and I own the technical roadmap, the delivery cadence that holds it, and the board conversation that goes with both.
Sold as a cadence rather than a day of my time, deliberately. What an early team needs is not eight hours of someone senior in the building — it is their judgement at the three or four points in a week where a decision otherwise gets made badly. And I am doing this job full time elsewhere, which is why the judgement is current: decisions I made this month, including about AI, rather than a playbook from a company I left in 2019.
What you get
- A weekly leadership session, in the diary, and async access between
- A technical roadmap tied to commercial milestones, and the cadence to hold it
- The technical section of your board pack, written by me
Weekly session + async · rolling monthly · £3,500/month
Selected work
What actually changed
Roles I held rather than client engagements — the fractional practice is new. Same work, different label, and every number here is one a reference call would confirm.
3 yrs
On the original architecture, no rebuild
Propelr
CTO & technical co-founder
Proptech · pre-seed to seed+ · 2023–now
Situation
A pre-seed proptech with a product thesis, no engineers, no platform, and enough runway to build one version of it.
What I did
- Built the entire technical platform from scratch and took it through to a seed-plus stage business, making the architecture and vendor decisions that a company at that size cannot afford to get wrong twice.
- Rolled AI tooling out across the engineering team — choosing what to adopt, where it genuinely helped, and the review practice around code nobody typed by hand.
Result
The platform carried the company from pre-seed to seed-plus without a rebuild. I am still the CTO, which is the strongest thing I can say about the decisions.
10→60
Engineers, in under two years
Marshmallow
Engineer → Senior Engineering Manager
Insurtech · employee 20 · 3 years
Situation
A car insurance startup heading for the round that would value it at $1.25bn, with under ten engineers and no engineering management function at all.
What I did
- I became the company's first engineering manager, then ran two teams and line-managed fifteen engineers plus a manager responsible for ten more.
- The founders chose me as the company's Bar Raiser: over fifty interviews in six months, final-stage culture interviews on their behalf, and the first backend engineer, frontend engineer and technical lead hired for a new Budapest office.
Result
Engineering went from under ten people to over sixty without the bar dropping, and I hired and coached the third and fourth engineering managers who took it from there.
12 moTo build the function and hand it overVita Mojo
12 mo
To build the function and hand it over
Vita Mojo
Senior engineering manager
Hospitality tech · Series B · 1 year
Situation
A Series B business with engineers in London and Moldova, no engineering management function at all, and a raise to deploy on growing the team quickly.
What I did
- I built the management function outright — 1:1s, objectives, review and a levelling framework across seven cross-functional teams.
- I rebuilt their hiring loop on the Bar Raiser model, and coached a junior engineering manager running a team of sixteen in the Moldova office.
Result
They finished with a working management layer and a hiring process their own people could run without me. That was the brief: build something that does not need the person who built it.
£500kA year in third-party feesMarshmallow
£500k
A year in third-party fees
Marshmallow
Senior engineering manager
Insurtech · Efficiency team · 2021
Situation
The business was paying a third party to run its monthly instalments, on a contract with a hard exit in November 2021 and no replacement built.
What I did
- I led the Efficiency team to remove Premfina and launch our own monthly instalments product against the deadline.
Result
Shipped on the deadline with no issues in the first thirty days, and took about £500k a year off the fee line.
About
Who you would be hiring
I came to engineering sideways — eighteen months as a foreign direct investment lawyer in Guangzhou, then teaching myself to code — and I have been building and running engineering teams ever since.
I was the Money Advice Service’s first junior engineer on a team that grew past thirty, then spent three and a half years as the in-house product team for Forward Partners, an £81m fund, building and shipping for its early-stage portfolio. I joined Marshmallow as employee 20 and stayed through the round that valued it at $1.25bn — first as an engineer, then as its first engineering manager, and finally running two teams and acting as the company’s Bar Raiser while engineering went from under ten people to over sixty. Vita Mojo hired me after that to build their engineering management function outright.
Since 2023 I have been CTO and technical co-founder at Propelr, where I built the entire platform from pre-seed through to seed-plus and rolled out AI tooling across the engineering team. That is the work I bring to other founders: I am doing it now, not remembering it.
Where that happened
Propelr
CTO & technical co-founder
Built the platform from pre-seed to seed-plus, and rolled AI tooling out across the engineering team.
2023–now
Vita Mojo
Senior engineering manager
Hired to build the engineering management function outright, and rebuilt hiring on the Bar Raiser model.
2022–23
Marshmallow
Engineer → senior engineering manager & Bar Raiser
Employee 20. Engineering went from under ten to over sixty, through the round that valued the company at $1.25bn.
2019–22
Paws.com
Frontend engineer, then head of product delivery
Shipped the build-a-box proposition against an eight-week deadline.
2018–19
Forward Partners
Frontend engineer
The in-house product team for an £81m fund, building across its early-stage portfolio.
2015–18
Before that: Money Advice Service, 2013–15 — and eighteen months practising foreign direct investment law in Guangzhou, before teaching myself to code.
Writing
How I think about this
Two pieces on what AI has actually done to engineering teams — the delivery system, and the interview loop.
You don’t need fewer engineers. You need a different team.
AI moved the bottleneck from writing code to verifying it. Almost everything about how you grow an engineering team follows from that one fact.
4 August 2026
Your interview loop is testing a skill that no longer exists
Take-homes are dead, live coding is contaminated, and most teams have quietly stopped trusting their own process. Here is how I would rebuild it.
4 August 2026
Reference
What the people who hired me say
Alex was our first engineering manager and helped us grow the team to six engineering managers and 60 engineers. He acted as a Bar Raiser for hires across the entire company as we scaled to our billion dollar valuation. He led the delivery of our first non-motor insurance product, home insurance, assembling the team from scratch to deliver a finished product within six months.
Co-founder & Chief Architect · Marshmallow
Questions
The things founders ask on the call
You’re already a CTO somewhere. How does this work?
You’re already a CTO somewhere. How does this work?
I am, and I am not hiding it — I am CTO and co-founder at Propelr, and that is exactly why this is worth buying. You get someone making these decisions this month, including about AI, not recalling them from a company he left years ago. It also sets an honest ceiling: one engagement at a time, sold as a weekly cadence rather than a day of my time in your building. If you need someone there five days a week, I am the wrong hire and I will say so on the call.
Do I need an AI specialist instead?
Do I need an AI specialist instead?
If you are training models or building agent infrastructure, yes — hire an ML engineer, and I will tell you that on the call. But most teams asking this do not have a model problem. Gartner expects more than 40% of agentic AI projects to be cancelled by the end of 2027, and the failures are engineering and governance failures rather than model failures. What actually breaks is review practice, release safety, hiring standards and ownership. That is the layer I have spent six years running, and I rolled AI tooling out across my own team this year.
Why not just hire a full-time CTO?
Why not just hire a full-time CTO?
Eventually you should. But a strong full-time CTO costs £150k–£200k plus equity, takes four to six months to hire, and at pre-seed or seed you often cannot yet describe the role well enough to hire for it. I give you the judgement now, define the role properly, and then help you hire the permanent person.
What happens when we outgrow me being part-time?
What happens when we outgrow me being part-time?
That is the plan, and it is written into the engagement. I define the permanent role, sit on the loop as the senior technical voice, and hand over with a documented transition. Hiring the people who replace me is the part of this job I am best at — at Marshmallow I hired and coached the two engineering managers who took over from me.
What do you not do?
What do you not do?
I do not run technical due diligence, and I do not take on architecture audits of large existing systems — different specialisms, and you should hire someone who does them every week. I will not staff your project with an offshore agency, and I will not sign off on a plan I do not believe in to keep an engagement going. If the honest answer is that you need two more engineers rather than me, that is the answer you will get.