Overview

Day30 is seeking the first software engineer for a funded London startup. You will work directly with the two founders to build a platform that predicts subscriber behaviour and optimises paid acquisition for subscription apps.

What You’ll Do

• Design and build the platform from prototype to production-ready system
• Create intuitive interfaces for configuring clients' data connections, system monitoring, and streamlined client onboarding to reduce setup time
• Develop robust API integrations with 3rd party data sources. Examples include MMPs (AppsFlyer, Adjust, Branch) and ad platforms (Meta, TikTok)
• Build reliable connectors with proper error handling and incremental loading

• Architect high-performance data pipelines that scale with growing data volumes
• Optimise BigQuery operations for cost and performance
• Establish monitoring for pipeline health and data quality
• Establish CI/CD pipelines with automated testing and staged rollouts
• Implement infrastructure as code using Terraform or similar tools
• Design for scalability from a dozen clients to 100+ within 12 months

• Partner with the CTO on technical strategy and architecture decisions
• Collaborate with the Lead Data Scientist to productionise ML workflows
• Establish engineering best practices and development standards
• Mentor junior engineers through code reviews and pairing as the team grows

Requirements

• 4-6+ years building production systems with demonstrable business impact
• Strong full-stack capabilities: comfortable building frontend components and optimising data pipelines
• Deep expertise in Python and SQL with high code quality standards (e.g. ruff, mypy, uv, pytest, SQLFluff, pre-commit)
• Experience with backend API frameworks (Django preferred; FastAPI/Flask acceptable) and modern frontend frameworks (React, Vue, Svelte, Next.js, Tailwind)
• Proven track record with high-performance or real-time data processing
• Hands-on experience with cloud data warehouses (BigQuery, Snowflake)
• Right to Work in the UK (no visa sponsorship)
• Ability to work from Central London office 3 days/week

• Workflow orchestration tooling (Prefect, Airflow, Dagster)
• Data transformation tools (dbt) and data quality frameworks (Great Expectations)
• Infrastructure-as-Code (Terraform, Pulumi, or similar)
• Serverless compute (Cloud Run, AWS Lambda) and container orchestration (Docker, Kubernetes)
• Open source contributions or conference talks
• Ad-tech / mobile app / subscription business experience

You don't need to be an expert in everything from day one. A good candidate will have deep expertise in at least one area with a desire to learn across the stack.

Our Interview Process

• Application Review: CV, screening questions, and code samples to assess initial requirements
• Initial Screen (20 mins with CTO): Short video call to assess mutual fit and technical background
• Practical Exercise (take home, up to 2 hours)
• Technical Deep-Dive (60 mins, in-person): Discuss your solution, system design, and architecture decisions
• Founder Conversation (30 mins): Meet the founders to discuss motivations and career goals

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Benefits

Compensation & Benefits

• Base Salary: Up to £80,000 per annum (dependent on experience)
• Holidays: 25 days annual leave plus bank holidays
• Equity: Meaningful options as first engineering hire
• Flexibility: 3 days/week in Central London office, remote otherwise
• Equipment: Top-spec MacBook Pro and necessary tools
• Learning Budget: Conferences, courses, and resources to stay current

What Makes This Role Unique

• Founder-Adjacent Position: Work directly with two second-time founders and contribute to product direction and company culture
• Technical Ownership: Build core systems from near-scratch with autonomy over technical choices
• Immediate Impact: Your code ships to production quickly and directly affects client performance and revenue
• Growth Trajectory: Shape engineering culture as the first engineering hire