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Malt Strategy
Daniel CastrilloDC

Daniel Castrillo

Software Engineer

€800/day
San Sebastián, ES
8-15 years
Typescript
Node.js
Python
Next.js
JavaScript

Average response time: 1 hour

About Daniel

Generalist software engineer. I'm passionate about computing in all its facets, with a particular fondness for low-level systems — the terminal, databases, and developer tooling. Across my career I've worked in multiple industries, giving me a panoramic view of what it takes to build complex systems. I see communication as a fundamental tool for planning and clearing bottlenecks, and I focus on concrete, high-impact objectives that demand collaboration across multiple stakeholders.
Health and Wellness
Gaming and Animation
Public Sector

  • Spanish

    Native or bilingual

  • English

    Native or bilingual

  • French

    Basic

  • Japanese

    Basic

Can work on-site
San Sebastián (up to 50km)

Experience

  • Upwork
    Senior Software Engineer
    October 2023 - June 2026 (2 years and 8 months)
    • Co-designed and built an internal Claude Code plugin that migrated entire microfrontends to new design styles. Its validation process successfully migrated 80% of the platform to a new presentation in one month with minimal engineering resources.
    • Led frontend development of the Boosted Jobs and Ad Credits features, Upwork's core monetization features, in Nuxt 3, Vue.js, and GraphQL. Upwork's SEC 10-K filings cite these as a major driver of Marketplace take-rate growth from 13.8% to 18.0% on $662M revenue.
    • Migrated critical data-fetching from a legacy PHP monolith to GraphQL with Apollo, eliminating N+1 queries and cutting average API response times by 20%; raised test coverage from 40% to 90% with a Cypress end-to-end (E2E), Jest, and Vitest strategy the frontend guild still uses.
    Nuxt.js Claude Code PHP GraphQL Snowflake
  • Tecnologia Urbana
    Lead Software Engineer
    January 2023 - December 2023 (11 months)
    • Coordinated a team of three developers to build a real-time traffic monitoring system processing 1080p video from 50 cameras across 5 cities. We built the graphical interface with Next.js and NestJS and a Go pipeline carrying the camera feeds to the NestJS platform — the Go service processed the raw video on the server with OpenCV and sent the processed results to our NestJS backend.
    Next.js NestJs OpenCV GO React.js
  • Lantum
    Senior Software Engineer
    June 2021 - January 2023 (1 year and 7 months)
    London, UK
    • Redesigned the billing system while preserving its core logic, cutting support tickets by 50% — the reports were tied to traffic-congestion issues and locks blocking access to resources with cyclic dependencies.
    • Shipped drag-and-drop shift scheduling across web (React, TypeScript) and mobile (React Native) with availability management and conflict detection. 30,000+ National Health Service (NHS) workers use it to manage their rotas.
    • Replaced polling across 3 client apps with a GraphQL real-time subscription layer. Live shift availability, no page refresh needed.
    Django React.js React Native Redis JavaScript
Check out Daniel's experience

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Education

  • Developer, Information Technology
    Hack Academy
    2015
    Developer, Information Technology
  • Bachelor of Science in Psychology
    Universidad Metropolitana (VE)
    2015
    Bachelor's Degree, Psychology
Check out Daniel's education

Skill set

React.js
Rust
Ruby
Qwik

Categories