Sophia Castillo, web developer

Sophia Castillo

Web & Mobile,

Built by Sophia

I help entrepreneurs, content creators, and businesses turn their ideas into something extraordinary. Operating out of Washington, D.C., I team up with clients to whip up smart code and stunning designs. Let’s make something awesome together—working with me means you get a partner who’s all about creating cool stuff and seeing results. Pinky swear!

Currently working remotely from

Washington, D.C.

My journey as a software engineer started in a very unexpected way. I began my career as an actor, where I fell in love with storytelling, creativity, and human connection. Just like in acting, web development demands discipline, curiosity, and constant learning — and that’s what pulled me in. Now, I bring that same creative energy into my work as a developer, blending imagination with technical skill.

Languages: JavaScript, TypeScript, Dart, Python

Frontend: React.js, Next.js (App Router), React Native, Flutter, Tailwind CSS

Backend: Node.js, Express.js, REST APIs

Databases & ORM: PostgreSQL, Prisma, MongoDB, Firebase

Auth & Data: Firebase Auth, NoSQL & SQL data modeling

Cloud & Infrastructure: AWS (S3, RDS, basic infrastructure setup)

Sophia Castillo, Frontend Developer
Suprise!

Hi I'm Joey! I love to appear on my human's video-calls. She always tries to be professional with clients, but I do love to surprise her.

Joey, 4pawjay

What I Offer

🧠

Product-Minded Design & Engineering

I design and build digital products as living systems — intentionally structured to be discoverable, usable, and improvable over time.

Rather than treating websites and apps as one-time launches, I approach them as evolving products that support real business goals.

This means designing for clarity, performance, and measurable outcomes — so your digital presence doesn’t just exist, it works.

Best for: Founders, creatives, and small businesses who want a strategic digital partner — not just a developer.

🌐

Product-Driven Web Design & Development

Modern, responsive websites engineered to be conversion-ready — not just visually polished.
  • SEO-ready structure (page hierarchy, metadata, indexing)
  • Fast, mobile-first performance and accessibility
  • Conversion-focused layouts and user flows
  • Scalable architecture for future growth

Best for: Service-based businesses and personal brands focused on bookings, inquiries, or lead generation.

🛍️

Conversion-Focused E-Commerce Experiences

E-commerce sites built as sales systems — not templates.
  • Custom Shopify storefronts using the Storefront API
  • Squarespace setup and customization
  • Product and collection structure that supports discovery
  • Checkout flow optimization and conversion tracking

Best for: Brands that want their online store to convert better and scale with their product catalog.

📱

Mobile App Product Development

From concept to launch, I help turn ideas into functional, user-focused mobile products.

I build cross-platform iOS and Android apps from a single codebase, with thoughtful UX flows and strong performance.

Whether it’s an MVP, internal tool, or customer-facing app, I focus on building something people actually want to use — and improving it over time.

Best for: Startups, creators, and small teams validating or scaling a digital product.

📊

Product Insights & Analytics Setup

I set up the tools that help you understand how people actually use your site or app.
  • Traffic and conversion tracking setup
  • Key user actions measured (forms, bookings, clicks)
  • Search visibility and discovery insights
  • Clear, non-overwhelming reporting

Best for: Clients who want visibility into what’s working, what’s not, and where to improve next.

🔁

Ongoing Product Support & Optimization

Websites and apps shouldn’t stagnate after launch. This keeps your product improving.
  • Performance monitoring and technical upkeep
  • Analytics review and insight-driven refinements
  • Conversion and UX improvements over time
  • Light brand support (fonts, colors, Canva templates)

Best for: Clients who want a long-term digital partner, not one-off help.

Apple Keyboard
Breanna Calle
Working with Sophia was an absolute delight! She effortlessly brought my hair extensions website to life with her unparalleled expertise and creativity. The end result? A charming and stunning online space that truly reflects the essence of my business. I can't thank Sophia enough for her professionalism, patience, and unwavering commitment to excellence throughout the entire experience.
Read on LinkedIn
Breanna Calle, Owner at Carousel Hair Extensions
Marc Kase
We contracted with Sophia for React Native front-end iOS app development and she did a great job. Sophia has excellent communication and collaboration skills and was very easy to do business with. I hope to work with Sophia on more projects in the future...
Read on LinkedIn
Marc Kase, Fractional CIO & CTO at Achieve Agility, Inc.
Kirk Magnuson
I highly recommend Sophia as a front-end, React Native web developer. Her expertise in React Native and dedication to delivering high-quality code significantly contributed to the success of our projects at Kaptain. Sophia is a skilled developer, proactive problem solver...
Read on LinkedIn
Kirk Magnuson, Founder & CEO at Kaptain Outside App
Ryan Braun
She delivered professional level code on the back and front end of the project while contributing creatively to the scope. Her eye for detail and design were key throughout the development process. She delivered professional level code on the back and front end of the project while contributing creatively to the scope. Her eye for detail and design...
Read on LinkedIn
Ryan Braun, Senior Associate Technical Consultant at AHEAD
Chad Tao
The great developers don't become great entirely by themselves, and Sophia's humility is what I admire most about her. We need more professionals like Sophia. She did not have any technical background going into the bootcamp, but she showed tremendous growth throughout the course, and to this day continues to hone her skills and astonish me...
Read on LinkedIn
Chad Tao, Senior Software Engineer at Populus Media
Juanita Holley
It was an absolute pleasure working with Sophia. I appreciated her can-do attitude, her flexibility, and her intuitive nature. All members of our foundation were always pleased with the work she produced. Thank you again.
Juanita Holley, Board Member at Newport Beach Arts Foundation
Kevin Miller
I chose to work with Sophia on multiple web design projects because she is a studious coder, steadfast teammate, intelligent contributor, and a joy to work with. We also went through a rigorous process together of learning multiple coding technologies, libraries, and web design tenets...
Read on LinkedIn
Kevin Miller, Full-Stack Web Developer & Chemist at Agilent Technologies
Breanna Calle
Working with Sophia was an absolute delight! She effortlessly brought my hair extensions website to life with her unparalleled expertise and creativity. The end result? A charming and stunning online space that truly reflects the essence of my business. I can't thank Sophia enough for her professionalism, patience, and unwavering commitment to excellence throughout the entire experience.
Read on LinkedIn
Breanna Calle, Owner at Carousel Hair Extensions
Marc Kase
We contracted with Sophia for React Native front-end iOS app development and she did a great job. Sophia has excellent communication and collaboration skills and was very easy to do business with. I hope to work with Sophia on more projects in the future...
Read on LinkedIn
Marc Kase, Fractional CIO & CTO at Achieve Agility, Inc.
Kirk Magnuson
I highly recommend Sophia as a front-end, React Native web developer. Her expertise in React Native and dedication to delivering high-quality code significantly contributed to the success of our projects at Kaptain. Sophia is a skilled developer, proactive problem solver...
Read on LinkedIn
Kirk Magnuson, Founder & CEO at Kaptain Outside App
Ryan Braun
She delivered professional level code on the back and front end of the project while contributing creatively to the scope. Her eye for detail and design were key throughout the development process. She delivered professional level code on the back and front end of the project while contributing creatively to the scope. Her eye for detail and design...
Read on LinkedIn
Ryan Braun, Senior Associate Technical Consultant at AHEAD
Chad Tao
The great developers don't become great entirely by themselves, and Sophia's humility is what I admire most about her. We need more professionals like Sophia. She did not have any technical background going into the bootcamp, but she showed tremendous growth throughout the course, and to this day continues to hone her skills and astonish me...
Read on LinkedIn
Chad Tao, Senior Software Engineer at Populus Media
Juanita Holley
It was an absolute pleasure working with Sophia. I appreciated her can-do attitude, her flexibility, and her intuitive nature. All members of our foundation were always pleased with the work she produced. Thank you again.
Juanita Holley, Board Member at Newport Beach Arts Foundation
Kevin Miller
I chose to work with Sophia on multiple web design projects because she is a studious coder, steadfast teammate, intelligent contributor, and a joy to work with. We also went through a rigorous process together of learning multiple coding technologies, libraries, and web design tenets...
Read on LinkedIn
Kevin Miller, Full-Stack Web Developer & Chemist at Agilent Technologies
Breanna Calle
Working with Sophia was an absolute delight! She effortlessly brought my hair extensions website to life with her unparalleled expertise and creativity. The end result? A charming and stunning online space that truly reflects the essence of my business. I can't thank Sophia enough for her professionalism, patience, and unwavering commitment to excellence throughout the entire experience.
Read on LinkedIn
Breanna Calle, Owner at Carousel Hair Extensions
Marc Kase
We contracted with Sophia for React Native front-end iOS app development and she did a great job. Sophia has excellent communication and collaboration skills and was very easy to do business with. I hope to work with Sophia on more projects in the future...
Read on LinkedIn
Marc Kase, Fractional CIO & CTO at Achieve Agility, Inc.
Kirk Magnuson
I highly recommend Sophia as a front-end, React Native web developer. Her expertise in React Native and dedication to delivering high-quality code significantly contributed to the success of our projects at Kaptain. Sophia is a skilled developer, proactive problem solver...
Read on LinkedIn
Kirk Magnuson, Founder & CEO at Kaptain Outside App
Ryan Braun
She delivered professional level code on the back and front end of the project while contributing creatively to the scope. Her eye for detail and design were key throughout the development process. She delivered professional level code on the back and front end of the project while contributing creatively to the scope. Her eye for detail and design...
Read on LinkedIn
Ryan Braun, Senior Associate Technical Consultant at AHEAD
Chad Tao
The great developers don't become great entirely by themselves, and Sophia's humility is what I admire most about her. We need more professionals like Sophia. She did not have any technical background going into the bootcamp, but she showed tremendous growth throughout the course, and to this day continues to hone her skills and astonish me...
Read on LinkedIn
Chad Tao, Senior Software Engineer at Populus Media
Juanita Holley
It was an absolute pleasure working with Sophia. I appreciated her can-do attitude, her flexibility, and her intuitive nature. All members of our foundation were always pleased with the work she produced. Thank you again.
Juanita Holley, Board Member at Newport Beach Arts Foundation
Kevin Miller
I chose to work with Sophia on multiple web design projects because she is a studious coder, steadfast teammate, intelligent contributor, and a joy to work with. We also went through a rigorous process together of learning multiple coding technologies, libraries, and web design tenets...
Read on LinkedIn
Kevin Miller, Full-Stack Web Developer & Chemist at Agilent Technologies

Sleek Code.

Great Results.

Welcome to my showcase! Below, you'll discover a diverse collection of projects that embody my commitment to delivering innovative, high-quality solutions. From dynamic web apps to powerful SaaS platforms, each project reflects my passion for turning complex challenges into creative, precise outcomes. These endeavors not only highlight my technical skills but also my dedication to exceeding client expectations. I'm continually evolving, and so is this portfolio—stay tuned for more!

Featured Works

Rachael Johnson, HMUA
Rachael Johnson, HMUA
Carousel Hair Extensions
Rachael Johnson, HMUA
Beatbike Cycling
Rachael Johnson, HMUA
Sofi Tukker: Developer's Cut
Rachael Johnson, HMUA
Disney+ Reimagined
Rachael Johnson, HMUA
girl in red
Rachael Johnson, HMUA

Interested?

hi@builtbysophia.com

You’ve Got Questions — I’ve Got the Code

Hey Google
Hey Google ... assist me
Hey Google, call Sophia...

My Resume

Sophia Castillo, Developer ResumeView Resume
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That's it! Now it's your turn to say hi.
sophia@builtbysophia.com