David Marín, Developer in Cobeña, Spain
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David Marín

Verified Expert  in Engineering

Software Developer

Cobeña, Spain
Toptal Member Since
July 2, 2015

David is an open-source and open-data enthusiast with more than 23 years of experience as a professional developer. He has acquired various skills, including web programming (PHP and JavaScript), C, C++ (under Linux and Windows), and systems management. Of these skills, David specializes in web programming and has full-stack experience with Symfony PHP-based back ends, jQuery front ends, and WordPress/WooCommerce-based sites.


Dark House Development
WordPress, Zapier, APIs, WooCommerce, WooCommerce Database...
Fundación MAIOR
WordPress Plugins, Web Hosting & Domain Setup, WooCommerce, Debian, PHP...
The Healthy Mummy
JavaScript, WordPress Plugins, Web Hosting & Domain Setup, Docker, Selenium...




Preferred Environment

JavaScript, Linux, Symfony, LAMP, PHP, WooCommerce, WordPress, European Union (EU), VAT Return Preparation

The most amazing...

...algorithm I've developed is the control system for the automatic ventilation in Madrid Calle-30, a network of more than 40km of urban tunnels.

Work Experience

Freelance Back-end Specialist

2020 - PRESENT
Dark House Development
  • Worked on the back-end side for several web projects where I linked several services using their APIs, including Salesforce and Zapier.
  • Fixed several problems with WooCommerce Subscriptions.
  • Implemented custom plugins for several projects, mainly based on the back end.
Technologies: WordPress, Zapier, APIs, WooCommerce, WooCommerce Database, WooCommerce Subscriptions 2, WordPress API, WordPress REST API, WordPress LMS, WordPress Plugins, Salesforce API

Pro-bono System Manager | Web Developer

2003 - PRESENT
Fundación MAIOR
  • Managed a network of five Windows computers and a Linux file and mail server remotely.
  • Developed and deployed www.maior.es using WordPress and WooCommerce.
  • Developed and deployed www.amaysirve.es using WordPress and developed a template from scratch using Twig and Timber plugin.
Technologies: WordPress Plugins, Web Hosting & Domain Setup, WooCommerce, Debian, PHP, WordPress, CSS, Domains & Hosting, Full-stack Development, Web Development, User Experience (UX), Software Architecture

Web Lead Developer

2016 - 2024
The Healthy Mummy
  • Developed multiple custom features for the company website based on WordPress and WooCommerce.
  • Cleaned and optimized legacy source code to adapt it to the usage of good practices.
  • Developed multiple patches and improvements for several existing WordPress and WooCommerce plugins.
  • Implemented an automated test suite with Selenium to track the working conditions of the site.
  • Debugged and supported a variety of hosting problems.
  • Led a team of three developers working on the site's front and back ends.
  • Contributed to VWO tests to improve site conversions.
  • Led the effort to carry out the needed adaptations to migrate the sites from PHP 5 to PHP 7 and from PHP 7 to PHP 8.1.
  • Adapted all customizations to use the new WooCommerce High-Performance Order Storage (HPOS) database schema.
Technologies: JavaScript, WordPress Plugins, Web Hosting & Domain Setup, Docker, Selenium, MySQL, PHP, WooCommerce Subscriptions 2, WordPress, WooCommerce, CSS, APIs, WordPress API, Marketo, ACF PRO, Advanced Custom Fields (ACF), AffiliateWP, Amazon S3 (AWS S3), Amazon Web Services (AWS), Apache, Amazon EC2, Ajax, Klaviyo, BrainTree, PayPal, Domains & Hosting, Ubuntu, PHP 7, Linux Server Administration, Full-stack Development, Integration, Libcurl, eCommerce, Marketplaces, User Interface (UI), Web Development, Stripe API, Stripe Connect, Back-end Development, REST APIs, Cloudflare, WordPress Themes, Architecture, Leadership, Figma, Affiliate Marketing, User Experience (UX), Client Portals, Dashboard Design, Stripe Marketplace, Technical Architecture, API Integration, Data Engineering, Software Architecture, Technical Leadership, Payment Processing, Stripe Payments, Content Delivery Networks (CDN), Search Engine Optimization (SEO), Responsive Web Design (RWD), Load Time, Performance, Web Performance Optimization (WPO), Website Performance, Online Payments, Pixel Perfect, Google Cloud Platform (GCP), Code Review, SEO Tools, Site Speed Optimization, Amazon CloudFront CDN

Web Developer and System Administrator

2015 - 2023
Navigate Oceania
  • Fixed problems in a multi-domain site where the content should be replicated on all the sites.
  • Fixed a hacked WordPress installation and improved the site security.
  • Added space for advertisements on all the site pages.
  • Fixed problems with the translation plugin on the site.
  • Updated and cleaned up the plugins used on the site, as many of them weren't needed.
  • Migrated several sites from PHP 5 to PHP 7, and later from PHP 7 to PHP 8, and made the needed adaptations.
Technologies: WooCommerce, JavaScript, WordPress Plugins, Web Hosting & Domain Setup, PHP, WordPress, Domains & Hosting, PHP 7, Full-stack Development, Web Development, User Experience (UX)

Freelance Website Developer

2020 - 2021
Punch Buggy
  • Built a custom WooCommerce plugin to connect one site against the AmWin stock management system for a motorbike-shop site.
  • Used the WooCommmerce Composite Products plugin and built a customized system to build lures from many pieces. The interface included a preview of the generated lure based on the user's selections. This was for a fishing-apparel shop eCommerce site.
  • Built a system to manage shipments from scratch for an important furniture marketplace site built using CraftCMS, using Shippit to centralize shipments. The system calculated exact costs and estimated shipment durations.
  • Created the back end used by vendors to totally manage their part orders for a marketplace site.
  • Implemented several pages on the CraftCMS site, following mockups provided by the designer.
Technologies: PHP, WordPress, WooCommerce, WooCommerce Subscriptions 2, Craft CMS, Web Development, Back-end Development, REST APIs, User Experience (UX), Client Portals, Dashboard Design, API Integration

Woocommerce Developer | Payment Gateway Specialist

2020 - 2020
Belfort Design Agency
  • Developed from scratch a new payment gateway for WooCommerce to receive payments using Stripe Wire Transfer API.
  • Enabled the plugin orders as fully paid once the corresponding payments were received correctly.
  • Assisted with the site launch and fixed some problems related to the theme and general WordPress/WooCommerce configurations.
Technologies: WordPress, WooCommerce, Payment APIs, Braintree API, Web Development, Stripe API, Stripe Checkout, Back-end Development, REST APIs, User Experience (UX), Client Portals, API Integration, Stripe Payments, Online Payments, Pixel Perfect


2020 - 2020
Waterin Whole Limited dba Our Natural Environment
  • Developed a PDF Generator system that transforms a crafted HTML document into PDF format using wkhtmltopdf.
  • Enabled the system to retrieve the data for the different documents using calls to an existing API through Libcurl.
  • Implemented the system as a web service in PHP 7.
Technologies: Web, PDF, wkhtmltopdf, HTML, CSS, PHP, Libcurl, Domains & Hosting, Back-end Development, REST APIs, User Experience (UX)

Web Developer

2016 - 2016
Adapt Marketing
  • Corrected several problems using WordPress API due to an attack on the server.
  • Set up a web page using WordPress and WooCommerce, including selecting and adding plugins and generating custom plugins for specific features.
  • Migrated Photoshop designs to HTML/CSS using a newly developed WordPress theme.
Technologies: WordPress Plugins, Web Hosting & Domain Setup, Linux, WooCommerce, WordPress, CSS, Domains & Hosting, Full-stack Development, Integration, eCommerce, Web Development, WordPress Themes, User Experience (UX), WordPress Design

Web Developer

2016 - 2016
Meridix Creative, Inc.
  • Modified a website so it now uses Stripe payment gateway instead of PayPal's Payflow API.
  • Altered the style of several pages on the website.
  • Detected several security-related issues and started tasks to solve them.
Technologies: JavaScript, Web Hosting & Domain Setup, Stripe, Microsoft SQL Server, Azure, PHP, Domains & Hosting, Full-stack Development, Integration, Web Development, Stripe API, Stripe Checkout, REST APIs, Stripe Subscriptions, User Experience (UX), Payment Processing, Stripe Payments

Web Developer

2015 - 2016
  • Adapted the site to use the Braintree payment gateway.
  • Worked on security clean-up for the whole site, removing several security issues as potential SQL injection points.
  • Developed new features involving back-end and front-end modifications.
  • Worked on a different project, implementing a PHP-based API server to be consumed by the JumpOff mobile app.
Technologies: JavaScript, Web Hosting & Domain Setup, HTML, MySQL, PHP, Domains & Hosting, Integration, Web Development, REST APIs, User Experience (UX), API Integration

Software Developer | System Manager

2006 - 2016
  • Led a team of four to develop and deploy a proprietary reporting system for Canal de Isabel II, Madrid's public drinking water supplier.
  • Managed a three-person team to develop and deploy SICE Nautilus, a web-based operational assistance system that includes incident support and fleet, inventory, and maintenance management.
  • Optimized queries and made back-end improvements for a web-based report system for SICE's ITS solution. The improvements allowed the generation and exporting of reports involving huge quantities of data to PDF or Excel.
  • Worked on the water control system for the Segura Basin. Analyzed, designed, and implemented new features for the Basin Control Center, including interfacing with an automatic telephone service, C++, Aspen InfoPlus.21, SCADA, and an Oracle database.
  • Analyzed, designed, and implemented an automated calculation system using Java and ANTLR tool and other Java modules for the back end of a SCADA system for the auscultation of a dam against a MySQL DB. Deployed in Ebro Basin and dams control systems.
  • Developed new features for the Basin Control Center of the Tagus Basin. Deployed the new communication system and network of over 200 embedded x86-based Linux remote units. Built remote administration and updated features for these remote units.
  • Created automatic ventilation algorithms for the tunnel control system of Madrid Calle-30. Worked on RCU remote control systems, focusing on ventilation and fire detection subsystems.
  • Developed features aimed at improving the scalability and robustness of the remote control unit to support a larger number of I/O signals and connections (C++ for embedded Linux system using x86 arch). This was for the In Madrid Calle 30 project.
  • Deployed and managed internal Linux and Windows servers (CVS, SVN, Git) for the development department.
Technologies: ANTLR, SCADA, Highcharts, DataTables, NHibernate, ASP.NET MVC, Git, Subversion (SVN), CVS, Linux, Infoplus WMS, Microsoft SQL Server, MySQL, Oracle, PostgreSQL, Java, C++, C, Leaflet, jQuery, Symfony, JavaScript, PHP, Debian Linux, Ubuntu, Symfony 2, Linux Server Administration, Full-stack Development, Web Development, Architecture, Leadership, Dashboard Design, Technical Architecture, Software Architecture, Technical Leadership, Learning Management Systems (LMS), Drupal, Mobile Development, Responsive Web Design (RWD), Technical Writing, Email

Web Developer and Technical Consultant

2010 - 2012
Miguel Buckenmeyer & Co.
  • Created, installed, and managed several WordPress sites.
  • Integrated a web-based file manager in a PHP custom site and helped solve problems in it due to using Java-based plugins.
  • Provided technical assistance for different projects.
  • Customized an advanced WordPress template, implementing a grid design for the articles.
  • Tweaked a PHP-based website for a Spanish perfume company, solving some problems and programming some new features.
Technologies: WooCommerce, Web Hosting & Domain Setup, CSS, HTML, WordPress, PHP, Linux Server Administration, Full-stack Development, Web Development, WordPress Themes, User Experience (UX), Learning Management Systems (LMS), CTO, WordPress Design

Manager of Version Control Systems | C++ Developer

2005 - 2006
  • Led the integration management effort for all Movistar prepayment projects (Spain and Latin America) and the administration of several Linux and Solaris CVS servers.
  • Contributed to the implementation of new features for the Movistar Spain prepayment project. This involved C++ multi-architecture development and an extensive use of C++ templates.
  • Managed configuration integration systems and servers for the project.
Technologies: C++, CVS, Debian Linux, Ubuntu, Linux Server Administration

Web Developer | Project Leader | Systems | Database Manager.

2003 - 2005
Desarrollo y Recursos
  • Contributed to the administration, automation, and modernization of web (Apache+MySQL+PHP) and mail servers (Sendmail + Dovecot). Helped define policies for security, configuration management, development, and backups.
  • Developed a custom workflow and file management system for San Carlos Clinic Hospital (Madrid, Spain) using PHP for web programming and FDF for printable/electronic forms.
  • Designed and implemented an online showcase for Diputación de Jaén.
  • Analyzed, designed, and implemented customized services for www.iea.es.
  • Worked on the analysis, design, and implementation of a service for getting optimal routes between museums.
Technologies: JavaScript, Web Hosting & Domain Setup, Dovecot, Apache, Sendmail, Debian, PHP, Debian Linux, Linux Server Administration, Full-stack Development, Integration, PDF, Web Development, REST APIs, User Experience (UX), Email, WCAG

Co-owner | System Manager | Software Developer

2000 - 2003
Advanced Software Production Line
  • Helped install, manage, support, and boost security in Debian GNU/Linux servers and firewalls for small and medium enterprise environments.
  • Managed projects and analyzed, designed, and implemented AF-Architecture, a multi-tier modular architecture for enterprise software development under GPL open license. The project web page was programmed using a PHP-based app, TYPO3.
  • Analyzed, designed, and implemented a CMS system for the firm web page (www.aspl.es) using PHP.
Technologies: Web Hosting & Domain Setup, C, Debian Linux, Linux Server Administration, Web Development, Technical Architecture, Software Architecture, Learning Management Systems (LMS), CTO, Email

The Healthy Mummy Websites

A set of websites based on WordPress and WooCommerce, including one main eCommerce site with millions of orders and thousands of active users. Working on this project for more than seven years, I've been the lead developer for these sites.

I started the project cleaning and optimizing lots of legacy code that made the page slow, setting the usage of good practices. We achieved the speed targets.

I also developed multiple custom features to comply with marketing team requirements and multiple patches and improvements for WordPress core and several existing WordPress and WooCommerce plugins.

I developed several custom reports, implemented using low-level complex SQL queries.

I implemented an automated test suite with Selenium to track the working conditions of the site.

I debugged and supported a variety of hosting problems, successfully identifying several bottlenecks in the code.

I led the effort to carry out the needed adaptations to migrate the sites from PHP 5 to PHP 7 and then to PHP 8.1

I adapted the whole set of customizations to use the new WooCommerce HPOS database schema (High-Performance Order Storage).

I successfully migrated the site among several hosting platforms with minimum downtime.


I developed the shipping subsystem for this marketplace site based on CraftCMS, developing a plugin to allow the calculation of shipping prices and estimated time lengths using the external Shippit API services.

I also developed the back end for vendors for this site so that they can keep track of orders and past orders. They can also manage the corresponding shipments, sending the corresponding e-mail messages to final customers.

Ama y Sirve

The design and implementation of the website for this periodical bulletin, using WordPress, IssueM, and other plugins. Using a responsive theme, the site was designed from scratch using Twig and Timber, and a specific theme template was implemented for sending overviews of just-released issues using email marketing tools.

Linux Audit and Monitoring System

I developed a Linux audit and monitoring system for a startup based on a pre-loaded library and PAM module that captured all the executed commands and their generated output and sent them to an API for later consumption.

Hyperbaric Store

I developed a whole eCommerce website using WordPress and WooCommerce with other plugins.

I built a new theme translating Photoshop mockups into the corresponding HTML, CSS, and JavaScript routines.

Reporting System for Canal de Isabel II

A new report generation system for Canal de Isabel II, Madrid, Spain's main public water supplier.

I used C#, ASP.NET, the MVC framework, NHibernate, and Microsoft Excel for the back end. For the front end, I used a single Sage application with React and Bootstrap.

Nautilus: Web-based Operational Assistance System

I was the main designer and developer of this modular web system that provides all needed features for supporting infrastructure operation and exploitation: event and incident management, fleet management, stock control, preventive and corrective maintenance, and shift management and works management. Different modules can be installed based on the requirements of each project.

SIDERA Reports: Web-based Reporting System for SICE's ITS Solution

A web-based report system for SICE's ITS solution. I acted as the main designer and developer of this solution. It provides several reports related to traffic management that are shown on the web or can be exported to Excel or PDF formats.

Fundación MAIOR Website

A web page for an NGO using WordPress with several plugins and WooCommerce for the online shop.
To keep some information, I made adaptations and customizations of a purchased theme and several custom post types.

GnoMint: Open-source Tool for the Management of an X.509 Certification Authority

I was the project leader and main developer.

GnoMint is a tool for easily creating and managing certification authorities. It provides fancy visualization of all the information pertaining to a CA, such as x509 certificates, CSRs, and CRLs. GnoMint is currently capable of managing a CA that emits certificates that can authenticate people or machines in VPNs (IPSec or other protocols), secure HTTP communications with SSL/TLS, authenticate and cipher HTTP communications through Web-client certificates, and sign or crypt email messages. It's programmed in C using GTK+, SQLite, and GnuTLS libraries.

The project was created as the final-year project of my master's degree in computer science engineering.

Kelly Doe Studio Website

A website based on WordPress software. The website was mainly based on pictures of designs made by the studio. The base template was totally transformed, so the main page showed a very different grid-based layout for the main page.

Calculation Engine for Damdata: Dam Auscultation SCADA

The design and full implementation of a calculation engine programmed in Java for DamData: Ofiteco's specialized dam auscultation SCADA. The formulas are expressed in a formula definition language that is defined formally through lexical and syntax grammar. These formulas are compiled into grammar trees through compiler classes generated using ANTLR. The formulas are invoked by the SCADA and allow different calculations using current and historical data.

Madrid Calle-30 Urban Tunnels

In the context of the construction of Madrid Calle-30 tunnels (a 47 km urban tunnel network) and the development of its control system, I was responsible for analyzing, designing, and developing the ventilation algorithms for activating and controlling the different fans and ventilation-related equipment in the tunnels, following the guidelines marked by experts in the field.

I also worked on improving the scalability and robustness of SICE's RCUs (Linux-embedded systems based on x86 architecture) so that they could manage and control more than 9,000 analog and digital inputs and outputs.

Employee Portal for Hospital Clínico San Carlos (Madrid)

The system allows employees to start different procedures (asking for vacation, notifying of changes in a family situation, taxes, etc.) that involve several steps of bureaucracy. In every step, the assigned group of people is notified about the pending actions, allowing them to interact with the application.

I used PHP and MySQL in the server and PDF and FDF for the forms.

Routing Calculator for Huexpo.net

Amidst the development of an institutional website for the different museums in the province of Huesca (Spain), I developed a routing engine for calculating optimal routes for visiting the different selected museums. Based on the traveler's algorithm, the different routes were pre-calculated to ensure a fast response to the user.
1998 - 2003

Master's Degree in Computer Science

Universidad Politécnica de Madrid - Madrid, Spain


Software Security

The University of Maryland via Coursera


WooCommerce API, WordPress API, REST APIs, jQuery DataTables, Braintree API, Doctrine, jQuery UI, jQuery, React, Stripe API, Stripe, X (formerly Twitter) API, OpenStreetMap API, Leaflet, WordPress REST API, Highcharts, Infusionsoft API, Libcurl, LibC, GLib, OpenSSL, Stripe Connect, Salesforce API


ACF PRO, Advanced Custom Fields (ACF), Subversion (SVN), CVS, AffiliateWP, Stripe Checkout, GitHub, Bitbucket, GTK+, Exim4, Apache, DataTables, Redmine, Braintree SDK, wkhtmltopdf, Sendmail, Handsontable, Git, Bower, SoapUI, Nagios, ANTLR, Turbo Pascal, Composer, Microsoft Visual Studio, Google Analytics, Infusionsoft, AWS ELB, Amazon ElastiCache, Metorik, Figma, GTK, Zapier, Amazon CloudFront CDN


Symfony 2, Symfony, .NET, BEEP, ASP.NET MVC, Selenium, Bootstrap 3, ASP.NET MVC 4, NHibernate


PHP 5, HTML, PHP, C, HTML5, JavaScript, CSS, PHP 7, C++, CSS3, Bash, Bash Script, SQL, Visual Basic 6 (VB6), C#, Java, Assembler, Modula-2


WooCommerce, WordPress, Debian Linux, Linux, Ubuntu, LAMP, Web, Marketo, Debian, Azure, Docker, Embedded Linux, Android, Oracle, Windows, Amazon Web Services (AWS), Amazon EC2, VWO, WordPress Theme Design, Klaviyo, Linux RHEL/CentOS, Craft CMS, Drupal, Google Cloud Platform (GCP)


WP Engine, JSON, MariaDB, PostgreSQL, MySQL, MySQL Server, Databases, Microsoft SQL Server, Amazon S3 (AWS S3), Database Security, Redis, SQL Performance, WooCommerce Database


Model View Controller (MVC), Web Architecture, Web Performance Optimization (WPO), Hosting, Unit Testing, Responsive Layout, Responsive, Search Engine Optimization (SEO), Conversion Rate Optimization (CRO), Security Software Development, Compiler Design, Concurrent Programming, Agile Software Development, Mobile Development, Responsive Web Design (RWD)


APIs, Web Hosting, Web Hosting & Domain Setup, Domains & Hosting, Local Hosting, Embedded Software, Unix Shell Scripting, gnoMint, WordPress Plugins, WooCommerce Subscriptions 2, eCommerce, Architecture, BrainTree, Content Management Systems (CMS), WordPress Themes, Full-stack Development, Integration, Web Development, API Integration, Software Architecture, Payment Processing, European Union (EU), Online Payments, Legacy Code, Legacy Software, CAPTCHA, Ajax, GNU, TCP/IP, X.509, SOAP, Client-server Model, User Interface (UI), Payment APIs, Payment Gateways, Technical Leadership, Technical Reports, Query Composition, Query Optimization, Linux Server Administration, Stripe Payments, WordPress Design, Back-end Development, Back-end, Marketplaces, Cloudflare, Affiliate Marketing, User Experience (UX), Technical Architecture, Data Engineering, VAT Return Preparation, Load Time, Performance, Website Performance, CTO, Email, Code Review, Infoplus WMS, SCADA, Dovecot, Image Manipulation, Embedded Systems, Linux Kernel Drivers, IT Security, Security, Payment Security, Shops, Search, Responsive Design, Responsive UI, Email Marketing, Email Marketing Automation, Google SEO, Organic SEO, SEO Tools, Data Visualization, Regular Expressions, Front-end, Front-end Development, Web Security, Programming, Compilers, Software Engineering, Distributed Software, Operating Systems, Microprocessors, Cryptography, Expert Systems, Networking, IP Networks, Internet Protocols, PayPal, PDF, Reports, SSL Certificates, X.509 Certificates, GnuTLS, RTLinux, Supervisory Control & Data Acquisition (SCADA), Document Management Systems (DMS), Employee Benefits, Dokan, Commerce, Amazon RDS, PHP Performance, Shippit, Leadership, Stripe Subscriptions, Client Portals, Dashboard Design, Stripe Marketplace, WordPress LMS, Learning Management Systems (LMS), Content Delivery Networks (CDN), Technical Writing, Pixel Perfect, Site Speed Optimization, WCAG

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