MARK GUERRERO

EXPERIENCE

• Present May 2024

  SENIOR FULL-STACK SOFTWARE ENGINEER

  COMPANY CONFIDENTIAL

  Full-stack engineer on a team of 3 developers and 2 QA engineers building two greenfield platforms, Donor Plus and Dispatch IQ, on React Native, TypeScript, Node.js, C#/.NET with Entity Framework, SQL Server, and OAuth. Own the functional design and key technical decisions, partnering with the product owner and designer.

  • Delivered Donor Plus, live for over a year with 10,000 registered users, and its admin portal, which stakeholders use to compose and schedule notifications.
  • Designed real-time updates for Dispatch IQ (50 to 100 drivers, now in UAT): SignalR broadcasts each change, such as a driver status update, and React Query refreshes web and mobile screens instantly. Azure Functions with Expo Push send push notifications.
  • Championed accessibility on Dispatch IQ with the product designer, building to WCAG AA beyond the company’s Level A requirement: alt text, accessible labels, color contrast for text, icons, and inputs, visible focus states, clear headings and error messages, light and dark modes, and responsive text, verified with Lighthouse audits.
  • Built offline-first support with SQLite caching, background sync, and optimistic UI for drivers in low-signal areas.
  • Brought Trip API load time from about 3 seconds to under 500ms by tracing slow mobile calls to an N+1 query in the Entity Framework logs and rewriting it with joins, projections, and pagination.
  • Streamlined the photo flow from 5 taps to 3, brought camera launch under one second, and sped up signature uploads with parallel Azure Blob uploads.
  • Cut duplicate photo and signature records from roughly 1 in 7 uploads to fewer than 1 in 100 by adding idempotency keys.
  • Test with Jest and React Native Testing Library (unit and UI), Playwright (web and API end-to-end), and Postman (API), and fixed the failing Playwright suite.
  • Use a prompt engineering workflow that feeds product requirements and Figma designs into Claude (with Figma MCP) and ChatGPT to speed up feature development.
  • Stepped in to lead the team through a tight-deadline release, building the backlog, defining requirements, and assigning work.
  • Own the dev infrastructure (Expo SDK and .NET upgrades, CI/CD, EAS Build and Submit to the App Store and Google Play, certificate renewals) and wrote the onboarding architecture docs.
• Apr 2024 Jul 2021

  SOFTWARE ENGINEER, REACT / REACT NATIVE (CONTRACT)

  NUTRIEN

  Delivered features across UnifiedHub, a React, React Native, and Next.js monorepo on Node.js and GraphQL, used by farmers, crop consultants, and internal e-commerce teams.

  • Simplified and sped up the product search, cart, and checkout screens by eliminating unnecessary re-renders, lazy-loading noncritical data, and caching branch and sales data.
  • Brought seed and crop-input ordering into the mobile app so farmers could calculate how much they need against available inventory and order from the field.
  • Shipped features and fixes in the Simplified Work Order and Sales Document Work Order flows with backend, design, and product teams.
  • Resolved production GraphQL and UI bugs by refactoring custom Material UI and Bonsai components, which sped up later feature work.
• Jul 2021 Dec 2020

  SENIOR SOFTWARE ENGINEER, REACT / REACT NATIVE (CONTRACT)

  BOOM FANTASY

  Owned the admin tools behind contests and promotions for Predictor, NBC Sports, and Barstool Sports games, using React, React Native, Next.js, Node.js, Jest, Postman, and Kubernetes.

  • Rewrote the legacy Predictor admin from scratch in React and Next.js, giving the internal contest team one simple flow to set up contests, dates, and rules.
  • Launched contest creation in the new admin, which made contests easier to run and helped lift daily active players 15%.
  • Cut cross-product content updates from 20–30 minutes to 5–10 minutes with a new content-saving system.
  • Wrote a generator that builds live-feed schemas automatically from selection criteria.
• Dec 2020 Jan 2019

  SENIOR FULL-STACK SOFTWARE ENGINEER

  HCA HEALTHCARE

  Led a team of 3 developers modernizing two legacy healthcare apps handling HIPAA-protected medical records, using React, Redux, Material UI, React Native, Node.js, GraphQL, SQL Server, and C#/.NET.

  • Moved Patient Tracker to React Native on a GraphQL backend with Redis caching (API responses from 198ms to 10ms). The new tracker helped cut patient wait times from about 35 minutes to 5.
  • Halved patient registration time by moving Virtual Registration to React Native with a single intake flow for identity and HIPAA-required details.
  • Redesigned how patient-tracking data stays in sync for the care-coordination team.
• Jan 2019 Jun 2018

  LEAD FULL-STACK SOFTWARE ENGINEER (CONTRACT)

  STRATFS

  Led a team of 3 developers moving legacy C#/.NET apps onto Node.js microservices.

  • Cut server response times from 2–5s to 200–350ms with the new microservices.
  • Shortened QA deployments from about an hour to under 30 minutes by introducing Jenkins CI/CD with parallel pipelines, build caching that skipped unnecessary rebuilds, and fail-fast checks.
  • Moved source control from SVN to GitHub and brought in Heroku, Box, and OAuth.
  • Co-built a .NET and Node.js sales tool with MongoDB and OAuth for 10 to 15 reps that cut presentation prep from 30 minutes to 10.
  • Built a React and Socket.IO app that displays images and PDFs live during sales presentations.
• Jun 2018 Aug 2015

  SENIOR FULL-STACK SOFTWARE ENGINEER

  SCHLESINGER GROUP

  Worked across SAMS (the company's C#/.NET and SQL Server platform for projects and recruiting), its mobile app, and the company website. Learned React on side projects, then introduced it to the team as the replacement for AngularJS.

  • Migrated the mobile app from Angular to React Native.
  • Built a respondent tracker dashboard in React, Redux, and Material UI on a Node.js, TypeScript, and GraphQL backend.
  • Created the shared component library (React, Redux, Material UI, Styled Components) that later products were built on.
  • Integrated the OnDemand QualBoard API with no downtime, and built a reusable setup template that cut new-project configuration from 45 minutes to 15 and gave other developers a consistent starting point.
  • Led the migration of every IIS-hosted web app to Azure, reworked the integrations that didn't carry over, and trained and mentored the offshore teams.
  • Ran the US and EU platform rebrand and localization, including email templates, UI strings, and notifications.
  • Relaunched the company website in React and Redux with REST APIs, Google Maps, and ZIP code lookup.
• Aug 2015 Jan 2015

  APPLICATION DEVELOPER IV (CONTRACT)

  BANK OF AMERICA

  Worked on Prime Brokerage systems for client trade reporting and transaction processing across Swaps, ETF, and DTC, using C#, .NET 4.5, SQL Server, Oracle, and ExtJS.

  • Set up Jenkins continuous builds from SVN for the GPB, IPB, and CCI projects.
  • Built a Selenium functional UI test suite with the page object model, running on IE and Chrome from a single shared driver instance.
  • Introduced SpecFlow for behavior-driven development, with configurable smoke tests for the local, dev, and QA environments.
  • Built a multi-threaded C# tool that compares SQL Server and Oracle 9i scripts and exports the results to PDF and Excel.
  • Trained developers on writing object-oriented automated test scenarios.
• Jan 2015 Aug 2014

  SENIOR .NET DEVELOPER (CONTRACT)

  JPMORGAN CHASE

  Built Targeted Email, a tool for scheduling email broadcasts to recipient lists pulled by custom criteria, in C#, .NET 4.5, and ASP.NET MVC 4.

  • Added single sign-on with Windows IDs.
  • Built the queue-based Windows service that sends the broadcasts.
  • Turned uploaded documents into email-ready message bodies using Aspose.
  • Wrote automated tests with NUnit and SpecFlow, using Gherkin and the page object model.
  • Worked in Agile Scrum with domain-driven design, Entity Framework 4, and LINQ, tracking work in JIRA and SVN.
• Aug 2014 Feb 2013

  SENIOR .NET DEVELOPER

  SCHLESINGER ASSOCIATES

  Worked on SAMS, the company's project and recruiting platform, and led two new projects, Project Breakthrough and Infoboard.

  • Led Project Breakthrough, a redesign of the SAMS workflow and the team's first AngularJS single-page app on .NET Web API. Cut development time by nearly 40% by building reusable AngularJS directives for search and breadcrumbs, while adding infinite scroll, filtering, and validation and reducing server calls.
  • Designed and built Infoboard from scratch: a respondent app with expiring short links to open survey opportunities, and an admin site for setting up panels and targeting rules. Used Knockout, Bootstrap, and SignalR for real-time admin messaging.
  • Built an email suppression Windows service that flags bad emails, updates membership status, and shows live progress through SignalR.
  • Created a payment upload system that exports respondent payments to a vendor's SFTP folder.
  • Led EU support for SAMS, including French and German localization, translated email templates, and region-specific custom fields.
  • Added Client Portal updates from SAMS with file attachments, and built a client preference page in AngularJS in under a day.
  • Set up CI/CD in TFS with MSBuild so every check-in was built and deployed.
• Feb 2013 Jul 2011

  .NET TECH LEAD

  REVOLUTION DIGITAL

  Managed day-to-day development of .NET and PHP sites and Facebook campaigns for consumer brands including NUK, Gerber, Dial, Centrum, Renuzit, and Henkel.

  • Redesigned the NUK and Gerber sites and built Facebook promotions such as photo contests, parent reviews, and voting, where users entered with their email address.
  • Converted Facebook FBML sites to XFBML apps with like-gating, Open Graph, and a one-vote-per-day rule.
  • Rebuilt Flash modules on the Centrum site in jQuery and HTML5 so they worked across browsers.
  • Added a text-resize menu so visitors could enlarge fonts on the brand sites.
  • Integrated MailChimp sign-ups, the Google Search API, Google Analytics event tracking, and a feed reader pulling from Facebook, YouTube, and WordPress.
  • Handled monthly Facebook reporting and promotional updates for Dial and Centrum.
• Jul 2011 Mar 2011

  SENIOR .NET WEB DEVELOPER

  VERITEXT

  Led development of VIP21, a portal for searching legal transcripts, exhibits, assignments, and shared files, built in VB.NET and ASP.NET on .NET 3.5 with SQL Server.

  • Added full-text search, calendar scheduling with quick duplication and rescheduling, and transcript and exhibit uploads.
  • Gave the portal sortable, paged data grids and a consistent look using Infragistics controls and theming.
  • Fixed existing errors, added database error logging, and simplified the search pages.
  • Built a RESTful WCF service and modeled entities with Castle ActiveRecord and NHibernate for VIP Anywhere, the mobile and desktop redesign.
• Mar 2011 Nov 2009

  SENIOR .NET WEB DEVELOPER (CONTRACT)

  PFIZER

  Rebuilt the Advil and Caltrate websites and managed other brand sites, including ThermaCare, ChapStick, Centrum, Alavert, Anbesol, and Dimetapp.

  • Sped up the sites with ASP.NET data and output caching and fewer server round trips, tuning with YSlow, Firebug, and Fiddler.
  • Reorganized the code into reusable classes and XML-configured modules, and standardized data access and error logging on Microsoft Enterprise Library.
  • Added SEO-friendly URL rewriting and canonical URLs.
  • Hardened the sites with input validation, the Anti-XSS library, and SSL.
  • Added a text-resize menu so visitors could enlarge fonts and read the brand sites more easily.
  • Wrote T-SQL templates and functions to load and clean articles and FAQs, and built an alternate Advil redesign on DotNetNuke.
  • Handled deployments to development, staging, and production, including each environment's configuration.
• Sep 2009 Feb 2009

  PROGRAMMER ANALYST

  THE GMS GROUP

  Built an email newsletter app for creating newsletters, scheduling campaigns, and managing customer lists, in ASP.NET and VB.NET with a custom ADO.NET data library.

  • Modeled the requirements in UML, including use case, class, component, and state diagrams.
  • Designed the SQL Server 2005 tables, views, and stored procedures, with key and check constraints.
• Feb 2009 Oct 2008

  ASP.NET WEB DEVELOPER

  VANTAGE APPAREL

  Built Store Builder, which let customers run their own online stores with Vantage products and their own logos.

  • Gave the sales team a login to view customer contacts, sales orders, and inventory, and to set up stores for their clients.
  • Designed it as a three-tier, object-oriented app in VB.NET and ASP.NET on SQL Server 2005, with Crystal Reports.
• Sep 2008 Oct 2006

  ASP.NET DEVELOPER

  ROTHSTEIN KASS

  Improved how accountants and principals handled K-1s, from processing and document management to proposal approvals.

  • Built an alert system that warns staff before their CPA licenses expire.
  • Created an employee self-service app where staff update and validate their own information, with role-based editing.
  • Maintained the Legal Notification, New Hire, Employee Validation, and K-1 Management systems using VB.NET, ASP.NET, SQL Server, Reporting Services, and SSIS.
• Oct 2006 Jun 2005

  ASP.NET SYSTEM SPECIALIST

  KNOWLEDGE SUPPORT SYSTEMS

  Helped finalize client requirements and lay out the structure of PriceNet, a pricing application.

  • Supported high-priority pricing model updates, price and volume elasticity analysis, data cleansing, reports, and client database maintenance using ASP.NET, SQL Server, T-SQL, DTS, SSIS, and OLAP.