Isaac Sanchez Aguilar.

Blend powers the entire process of collecting, validating, and analyzing loan and mortgage applications for U.S. banks — thousands of applications a day.

• Designed and shipped loan products across three families — bank lending, mortgage, and auto — end-to-end, from backend data models, services, and APIs to the frontend.
• Increased test coverage by 60% and optimized CI times by cleaning up unnecessary data and applying best practices.
• Delivered knowledge-sharing sessions on engineering best practices.
• Took part in on-call rotations for production lending systems handling regulated financial applicant data.

PayPal’s checkout is one of the highest-traffic payment flows on the web — the platform processed ~25B payment transactions and $1.5T in payment volume in 2023.

• Backend work on PayPal’s Checkout GraphQL layer: improved server monitoring and standardized error handling across resolvers, improving checkout error detection and transaction tracking by 60% and cutting false positives.
• Led the migration of currency and amount handling in the checkout flow to new libraries — a correctness-critical change on a live payments path — detecting and fixing the resulting bugs.
• Recovered 50% of the functional tests that were broken, restoring the regression signal for the checkout service.
• Took part in on-call rotations for the checkout platform.

Intermountain Healthcare is one of the largest health systems in the U.S. — patient-facing products built in a regulated healthcare environment.

• Led the migration of 100% of the React Native router in the mobile app, with zero regressions.
• Designed the application architecture and led the planning and implementation of new modules on web (React) and mobile (React Native).
• Mentored a team of roughly 10 engineers through code reviews, pairing, and onboarding.

• Built the entire Crediverso product ecosystem from scratch as part of an 8-engineer, 2-PM team — Python backend services and data models alongside the React frontend.
• Worked directly with clients across engagements — gathering requirements and coordinating with leads and product owners.

• Built full-stack features on a Node.js (Koa) + TypeScript backend with MongoDB, Redis, and Docker, plus React/React Native clients.
• Fixed Redis cache bugs and reduced the memory usage of a listing module by replacing a heavy virtual-DOM renderer with a sliding-window approach, and mentored teammates.

• Built backend and end-to-end test coverage in Hack and JavaScript for Facebook Ads flows.
• Developed internal models for detecting data mismatches across systems.
• Found and fixed production bugs surfaced through this testing.

• Co-built Bioderma’s internal system for managing promotions, sales, and distribution (mobile, web, and backend).
• Developed NestJS backend services and Vue.js/Quasar frontend features, worked across the Java and PHP parts of the codebase, and refactored toward clean architecture.