HELLO, WORLD.
I'm Callistus Nwachukwu.
SOFWARE ENGINERR | TECH-PRENEUR | FULL STACK DEVELOPER
About Me
Let me introduce myself
I am a Full Stack Web Developer and Software Engineer with expertise in building scalable web applications and SaaS platforms. Originally from Nigeria and currently residing in Lagos State, I have acquired a wide range of skills and certifications in web development. I prioritize data security, code readability, and application usability in every project I work on.
Skills
My core competencies include PHP, JavaScript, HTML5, CSS, and MySQL. I specialize in WordPress development, including custom plugins and themes, headless CMS implementations, and advanced REST API integrations. I also have a strong background in cloud deployments, leveraging technologies like Cloudflare Workers and Pages, and managing complex DNS infrastructure.
My Technical Skills
PHP
Advanced – 6+ years
JavaScript
Advanced – 5+ years
MySQL
Proficient – 5+ years
HTML & CSS
Advanced – 6+ years
WordPress
Expert – 6+ years
WooCommerce
Expert – 5+ years
Profile
My mission is to build innovative solutions that help small and medium-sized businesses increase profitability by automating time-consuming tasks. To support this vision, I developed the Smart Woo Service Invoicing plugin — a WooCommerce® extension that transforms a WordPress® site into a powerful service subscription and invoicing engine. I also maintain several other plugins and themes available on WordPress.org.
FULL NAME:
Callistus Nwachukwu
DATE OF BIRTH:
JOB:
Software Engineer – Frontend & Backend Developer, Web Application Architect, WordPress & DevOps Specialist
Website:
callistus.callismart.com.ng
Email:
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A Glimpse of My Journey
How I started
My passion for web development began in 2018 when I built my first blog using WordPress®. The struggle to find the right plugin for my needs sparked my curiosity—and frustration—which eventually led me to pursue web development alongside my career in electrical engineering.
One of my earliest side projects was a notification bell system for the WordPress admin dashboard. That experience introduced me to the WordPress ecosystem under the hood—and quickly fueled my interest in solving real-world problems through plugins.
Not long after, I started experimenting with service billing systems in WooCommerce. I realized that popular subscription plugins like WooCommerce Subscriptions and WP Swings lacked a true subscription abstraction—they were just recurring orders with no clear separation of services, lifecycles, or associated invoices.
That insight led to the creation of Smart Woo Service Invoicing—a purpose-built WooCommerce® extension that models real-world service subscriptions, automates invoicing, tracks usage, and supports prorated billing. It treats subscriptions as contract-based services, not just repeat orders.
Today, I serve as the CEO of Callismart Tech, where I lead the development of powerful WordPress plugins, custom web applications, and SaaS platforms that empower small and medium-sized businesses. I’m proud to have authored several tools available on the WordPress Plugin Repository, and I continue to build solutions that make complex tasks simpler and businesses more efficient.
My Motivation
My primary motivation is to make technology accessible and useful for businesses that need automation, clarity, and performance—but may lack the resources for full-scale enterprise tools. I aim to build scalable, user-friendly solutions that empower small and medium-sized businesses to focus on growth while I handle the complexity behind the scenes.
Whether it’s building a feature-rich plugin from scratch, fine-tuning performance for large-scale WordPress installations, or deploying serverless logic through Cloudflare Workers, my goal is always the same: simplify the workflow, enhance the experience, and unlock new possibilities through clean, maintainable code.
My Resume
My Professional Timeline
I am currently the founder of Callismart Tech and Callismart Electrical Company LtdExperience
Senior Web Developer
Part Time – 2020 to 2022
GTK World
I led a team of developers at GTK World® to build sales-driven web applications that boosted client revenue and retention.
WordPress® API Specialist
Full Time – 2021 to Present
Callismart Tech
I built private plugin/theme update infrastructure using WordPress® REST API. Architected custom tools for internal and client SaaS.
Lead Developer – Smart Woo Service Invoicing
Plugin Architect, Core Developer – 2023 to Present
Callismart Tech
I architected and currently maintain Smart Woo Service Invoicing — a WooCommerce® extension that introduces true service-based subscriptions, invoice billing, and usage metering. It was built from scratch to fix limitations in existing subscription plugins.
Custom Web App Developer – Private SaaS Platforms
Full Stack Engineer – 2022
Freelance / Internal Projects
I planned and built internal SaaS platforms using PHP, WordPress, and Cloudflare Workers — integrating payment gateways, user access control, and custom REST APIs to deliver secure, fast, and scalable web applications.
Open Source Maintainer – Smart Woo Plugin
Ongoing Contributor – Since 2023
WordPress Plugin Repository
I actively maintain and support the free version of Smart Woo Service Invoicing on WordPress.org. This includes issue triaging, updates, feature curation, and user support — helping other developers build billing solutions on top of my work.
Education
Senior Secondary School Certificate (SSCE)
Graduated – 2015
Comprehensive Secondary School Agbala
Completed my formal secondary education in Nigeria, where I built a strong foundation in mathematics and logical reasoning—skills that would later shape my journey into software engineering.
Certifications in Web Development
Ongoing Journey – Since 2020
Programming Hub & Self-Taught
Earned certifications in PHP, JavaScript, and full stack web development via Programming Hub. Much of my learning came from deep, self-guided exploration—through documentation, coding blogs, trial and error, and solving real-world business problems.
B.Sc. in Computer Science
Planned / In View
University (To Be Determined)
As part of my long-term academic goals, I plan to pursue a Bachelor's degree in Computer Science to deepen my understanding of computer systems, algorithms, and software architecture. While I'm already proficient in full-stack development through self-taught experience and certifications, I believe formal education will complement my practical knowledge and open more doors in the tech industry.
Contact Me
I'd Love To Hear From You
Please feel free to contact me. I check my emails regularly and will respond as soon as I get your email.Chat with me on WhatsApp
Start ChatSend Message
My Projects
What I've Been Working On
Here are some of the tools and products I've built — each solving a real problem.Smart Woo Service Invoicing
Type: WooCommerce ExtensionA powerful plugin that transforms your WooCommerce® store into a complete service subscription and invoicing engine. It brings real-world billing logic — like prorated billing, usage tracking, and contract-based subscriptions — into WordPress®.
ViewSmart License Server
Type: Internal API ProjectA custom-built software update system for private WordPress plugins and themes. Built using the WordPress® REST API, it powers seamless version control, license validation, and update delivery for distributed software.
Must-Use Plugin Loader
Type: WordPress Tool / SnippetA lightweight PHP solution designed to streamline WordPress® Must-Use (MU) plugin management. It allows you to organize MU plugins into their own dedicated subdirectories, rather than requiring all files to be directly in the main `mu-plugins` folder.
Internal ToolEmail Hosting & Deliverability System
Type: Internal InfrastructureA fully managed email hosting setup where I configured advanced DNS records — including SPF, DKIM, and DMARC — to ensure sender authenticity and improve inbox deliverability.
get in touchPHP Email Client for Brevo® API
Type: PHP Component / API IntegrationA lightweight pseudo HTTP-based email client written in PHP that integrates with the Brevo® (formerly Sendinblue) API. It supports sending dynamic emails, including HTML content, file attachments, and CC/BCC options — all via clean function calls.
get in touchLocation-Based Utility Framework
Type: PHP Component / Web App IntegrationI wrote a lightweight PHP component that automatically formats dates, currencies, and time zones based on the user's location and country. Though originally designed as part of a larger web application, this utility can stand alone as a portable framework.
get in touchCallismart Tech
Type: Company Website & Software PortalThe official website for Callismart Tech — my software development company. It serves as a central hub for product announcements, plugin documentation, updates, and licensing. Built from scratch with performance, clarity, and future scalability in mind.
Visit SiteGTK World
Type: Beauty & Cosmetic Ecommerce WebsiteAn elegant, conversion-focused ecommerce platform for GTK World — a Nigerian beauty and skincare brand. I handled everything from design to WooCommerce integration, building a seamless online shopping experience.
Visit SiteQainoc Studios
Type: Nollywood Production Company WebsiteA bold, media-rich site designed for Qainoc Studios to showcase their Nollywood movie projects, promote upcoming films, and host video content. Built with performance and visual storytelling in mind.
Visit SiteNew Covenant Altars
Type: Church WebsiteA full-featured church website developed for New Covenant Altars & Miracles Church Inc. The site includes media embeds, event info, online contact channels, and a mobile-friendly layout to serve its growing congregation.
Visit SitePersonal Portfolio Website
Type: Full Stack / BrandingThis very site you're browsing — hand-coded from scratch to reflect my technical skills, design sense, and personal journey. It features custom frontend routing, a clean UI/UX, dark-mode support, and is fully hosted on Cloudflare Pages.
You're on it 🤓…And Many More
Not all my work is publicly available. Some projects are internal tools, client-specific solutions, or still under active development.
If you'd like to see a tailored demo or learn more about what I've built, feel free to reach out.
get in touchMy Blog Posts
Articles I wrote
Here you can explore the articles I've written404
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