Fractional Senior Full-Stack Engineer/Technical Lead at Simply Done, Manchester, £Contract Rate

Contract: Initial paid technical audit, followed by 2 days per week for 3 months
Location: Remote (UK-based candidates only, UK timezone required)
Start date: ASAP
Day rate: Please provide your expected UK contractor day rate

We are seeking a Fractional Senior Full-Stack Engineer / Technical Lead to help prepare an established UK-facing B2B SaaS platform for commercial launch.
The product is already substantially built and is not a greenfield project. The immediate focus is to understand the existing codebase, assess production readiness, identify critical risks, and support the final hardening, testing, and stabilisation of the platform ahead of launch.
This role is suited to a senior UK-based contractor comfortable working within large existing systems, navigating unfamiliar codebases, and making pragmatic, high-impact technical decisions under time pressure.

Engagement Structure
The engagement will begin with a short, paid technical audit.
The audit will assess:

Codebase structure, maintainability, and technical debt
Security posture and authentication/authorisation model
Multi-tenant data isolation and GDPR considerations
Database and backend architecture (PostgreSQL)
Test coverage and critical production gaps
Production readiness risks
Recommended 30/60/90-day technical priorities
If successful, the engagement will continue on a fractional basis at approximately 2 days per week for an initial 3-month period.

What You’ll Be Doing:
Reviewing and understanding an existing SaaS codebase
Identifying and delivering launch-critical fixes and features
Strengthening authentication, authorisation, and tenant isolation
Reviewing backend logic, database design, and security-sensitive flows
Writing integration tests for key user journeys
Improving system reliability ahead of UK commercial launch
Refactoring where necessary with a focus on safety and stability
Supporting code reviews and technical decision-making
Helping establish engineering standards and best practices

Essential Skills
Senior-level full-stack engineering experience (UK-based contractor preferred)
Strong experience with Node.js, Express, TypeScript, PostgreSQL, React, and Next.js
Proven experience with multi-tenant SaaS platforms
Strong understanding of secure system design, RBAC, and data isolation
PostgreSQL expertise (schema design, complex queries, indexing, performance tuning)
Comfortable working in and improving existing production codebases
Strong Git workflow and pull request discipline
Practical testing experience (especially integration testing)
Security-conscious approach aligned with UK GDPR principles
Strong communication skills with both technical and non-technical stakeholders

Desirables
Redis / background job systems (e.g. BullMQ)
WebAuthn / passkeys
Object storage (S3, Cloudflare R2)
Experience preparing SaaS products for UK/EU commercial launch
Experience with sensitive or regulated data environments

What We’re Looking For
We are looking for a senior engineer who operates as a technical lead rather than a task executor.
You should be able to assess existing systems, identify risks, prioritise improvements, and guide a product from “functioning” to “production-ready for UK customers”.
This role is not suitable for junior or mid-level engineers who require heavy structure or close supervision. We need someone senior, independent, pragmatic, and detail-focused.

Application
Please submit your CV along with a short note covering:
Your experience with multi-tenant SaaS systems (preferably UK/EU contexts)
Examples of inherited or productionised systems you have stabilised
Your strongest backend, frontend, and database experience
Your expected UK contractor day rate
Your availability over the next 90 days

Pay: £2,000.00-£5,000.00 per month

Application question(s):

• What are your salary or day-rate expectations for this position?

Work Location: Hybrid remote in Manchester