John Aaron Nelson
Based in Uruguay; works US hours.
Senior engineer and technical lead for startups.
I've shipped growth, platform and AI tooling at Calendly, Pipedream and a YC startup — and I take on select consulting and project work.
Selected work
Full resume →Calendly
Senior Full Stack Engineer · Jan 2025 - Aug 2026
Revenue-impacting Growth initiatives for the category-leading scheduling product.
Shipped growth experiments and improved instrumentation, cutting iteration time from weeks to days.
More than $1 million in ACV in 2025
On the resumePipedream
Lead Frontend Engineer · Dec 2021 - Dec 2024
Core workflow-building experiences (editor, debugging, core UX) for a developer automation platform.
Led frontend engineering and a team of 5 as project lead on growth-driving initiatives.
Product adoption growth of >30%
On the resumeVoiz Academy
Fractional CTO · Jan 2024 - Jan 2025
Operations ran on Notion-based workflows.
Led the move to a production SaaS, hired and led an engineering team of 4, and recruited the next CTO.
A production SaaS serving 1,000+ users
On the resume
Ways to work with me
Join your team
Senior, staff, founding or lead engineer roles at startups.
Consulting & projects
Fractional CTO work, AI and MCP builds, and scoped projects.
Training
Hermes Training: teach your team to do more with AI.
Hands-on AI training for teams, offered as Foundations, the Build Series and Executive 1:1.
For engineers
Building MCP servers for real work, not demo day.
My practical, operator-first guide to designing, shipping, securing, and operating MCP servers in production.
For builders designing, shipping, securing and operating MCP servers in production.
Open source
Weft: red squiggles for teams of coding agents.
GitHub coordinates people at merge time. Agents need it at edit time. Weft streams every agent edit into one ordered log per repo and tells the agent, mid-edit, when it collides with another agent's work, so conflicts get resolved before a commit exists. One protocol for Claude Code, Codex, OpenCode and Hermes, built on Cloudflare Workers and Artifacts.
MIT licensed. My entry to Cloudflare's “build the next Git platform” competition, October 2026.
iOS apps
Small apps I build and ship myself.
Fícha
Flashcards for Rioplatense Spanish, the Spanish of Uruguay and Argentina.
Download on the App Store
Recent writing
All writing →
Red squiggles for agents: building Weft with Weft
GitHub coordinates people at merge time. Agents need coordination at edit time. Weft is my entry to Cloudflare's next-Git-platform competition, and the agents that built it were coordinated by it.
The end of web apps
AI-powered native app development is transforming software creation, making web apps and traditional project management increasingly obsolete.
Tidy, Offload, and the Shape of Personal Infrastructure
Notes from building a small pair of terminal tools: one that understands what is taking space on a machine, and one that safely moves the things that do not belong there.
How I work
Fifteen years of building software and leading teams, in three habits.
Straight answers.
I say what I think the right call is and why, including “we shouldn’t build this.” Clear tradeoffs early save teams weeks later.
Boring tools, on purpose.
I reach for the well-understood option over the impressive one. Systems a team can reason about ship faster and break less.
Real people, even with AI.
AI is a force multiplier, not a replacement for taste, judgment, or responsibility.
Hiring, or have a project in mind?
Tell me about the role or the problem. I read everything that comes in.
Have a project instead? Start a project conversation →