About the job

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• Full-time
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Open role

• Arithmos
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Frontend / Product Engineer (Founding)

Own the product surface that millions of people will use to build their first custom index.

London (hybrid) or Remote (UK/EU)Full-time£150,000–£170,000 base

• 1.0%–1.5% equity
• performance bonus
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About Arithmos

Arithmos is building the retail layer for direct indexing. We turn a plain-English idea into a transparent, rule-based portfolio with institutional-grade backtesting and analytics. Our goal is to make structured investing accessible to millions.

The role

This is a founding product engineer role. You will own the user experience that determines whether users understand, trust, and share what we’ve built. Your work directly impacts growth, activation, and revenue.

What you’ll do

Own the end-to-end frontend experience

• Index creation flow (prompt → portfolio → backtest)
• High-performance charting and data visualisation
• Public, shareable index pages
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Build growth-critical features

• “Clone this index”
• Performance comparisons vs benchmarks
• Social sharing and embedding
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Drive conversion and activation

• Reduce time to first index
• Improve clarity of outputs (performance, holdings, risk)
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Partner with growth on rapid experiments

• A/B tests on onboarding, UI, and messaging
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Ensure best-in-class performance

• Sub-second load times
• Smooth, responsive UI across devices
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Requirements

• 3–7+ years building high-quality web products
• Strong in React / Next.js / TypeScript
• Experience with data-heavy UIs (charts, dashboards, analytics)
• Product mindset: you care about user behaviour, not just code
• Ability to ship quickly and iterate under ambiguity
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Nice to have

• Experience in fintech / investing products
• Familiarity with charting libraries (D3, Recharts, TradingView, Highcharts)
• Experience building viral or consumer-facing products
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Why this role is exceptional

• Direct ownership of a category-defining product
• Massive upside via equity
• Work on a product with clear product-market fit potential
• Build something users actually use daily — not internal tools
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