# Sajjad Umar

> Backend engineer with ten years of production software, mostly Ruby on Rails, with code in more than 40 Rails apps, now building products end to end by directing AI agents in plain English. Lead backend engineer at UMAI, a restaurant platform used in 15+ countries, where he is building the Bug Machine, a pipeline that takes bug tickets to reviewed pull requests with agents, and improving how the team uses AI. Author of Ruby on Rails for Agile Web Development. Creator of Airlock, an open-source SDK that makes AI agent actions exactly-once and human-approvable. Runs a one-person game studio with AI agents: ten games built in 48 days.

Principle: Never cause a side effect more than once, and always be able to prove what happened.
Location: Lahore, Pakistan (works remote across time zones)

## Good fit for
- Staff or principal backend roles
- AI agent infrastructure and reliability
- End-to-end product building with AI
- Rails systems at scale
- Founding engineer work where the product touches money or the real world

## Experience
- Lead Backend Engineer, UMAI Restaurant Software (2022-03 to present): Rails monolith behind reservations, loyalty and guest data for thousands of restaurants in 15+ countries. 6,700+ commits. Availability caching, Reserve with Google feeds. Building the Bug Machine and improving AI usage across the team.
- Community Manager, RubyConf Pakistan (2022-07 to present): Manages and contributes to Pakistan's main Ruby on Rails community.
- Founder, SUMAR TECH (2019-02 to present): Freelance Rails work (ServiceLovers, The Test Request, LoopCom), then Wapas, Airlock and a ten-game studio.
- Senior Software Engineer, InvoZone (2021-08 to 2022-02): Rails and Vue.
- Senior Software Engineer, Nextbridge (2021-06 to 2021-08): Rails.
- Intern to Senior Software Engineer and Team Lead, Tiksom (2017-01 to 2021-06): Three promotions in four and a half years. Backend and Android for startup products in travel, fintech, IoT and subscriptions.
- Junior Software Engineer (intern), PlumZ Studios (2016-10 to 2016-12): Android and third-party APIs.

## Projects
- [Airlock](https://github.com/SUMAR7/airlock-python): Python SDK that gates irreversible agent actions, commits each one exactly once and keeps a tamper-evident audit trail. Status: v0.3.0 on PyPI, MIT.
- The Bug Machine: Pipeline at UMAI that takes a bug ticket to a pull request: agents plan, fix and challenge the change, CI checks it, then three people review, test and approve it. Internal, so there's no public link. Status: In production use since 2026.
- [Wapas](https://wapas.me): Restaurant loyalty platform: digital stamp cards, win-back campaigns and a tower game with real prizes. Rails 8, Hotwire, Solid Queue. Status: Live, used at Masosa.
- [Masosa](https://masosa.pk): A real samosa restaurant in Sheikhupura, opened 21 June 2025. Founder. Status: Open daily.
- [SUMAR_TECH Games](https://sumar7.github.io/): Ten original Android games in 48 days, directed through AI agents: Stack Drop, Rope Swing, Tick Town, Dribble Home, Spell Crane, Paperwind, Summit Haul, Mislaid, Paint Panic, Sparkbloom. Status: Eight live on Google Play, two in review (November 2026).
- [Ruby on Rails for Agile Web Development](https://about.sajjadumar.dev): Hands-on guide to Rails with Scrum and Kanban. Published by AVA, an Orange Education label, 27 August 2024. Status: Published.
- RevBits Ruby SDK: Gem and Puppet plugin for securely fetching secrets from RevBits PAM. Status: 2021.

## Writing
- [The double refund: why AI agents need exactly-once](https://medium.com/@sajjadumar/the-double-refund-why-ai-agents-need-exactly-once-319360705082)
- [AI Tools vs. AI Agents: The Shift Most Engineers Are Missing](https://medium.com/@sajjadumar/ai-tools-vs-ai-agents-the-shift-most-engineers-are-missing-8286fdc4de34)
- [Forget Writing Code for a Minute. Let's Talk About Reading It.](https://medium.com/@sajjadumar/forget-writing-code-for-a-minute-lets-talk-about-reading-it-ac928cac14a7)
- [Why I Still Bet on the Rails Monolith in 2025](https://medium.com/@sajjadumar/why-i-still-bet-on-the-rails-monolith-in-2025-01c3e62d491a)
- [The Senior Dev's Guide to Effective Database Indexing in Rails](https://medium.com/@sajjadumar/the-senior-devs-guide-to-effective-database-indexing-in-rails-2571ef6604b4)

## Machine access
- [Structured profile](https://sajjadumar.dev/me.json)
- MCP server (streamable HTTP, no auth): https://sajjadumar.dev/mcp

## Contact
- Email: sajjadumardev@gmail.com
- LinkedIn: https://www.linkedin.com/in/sumar7
- GitHub: https://github.com/SUMAR7