$ opex_ai_scorecard:
Designed + coded cross-org scorecard
Built an OPEX productivity scorecard to track AI adoption and measurable improvements across Walmart and Thermo Fisher.
marco-diaz@portfolio:~
Terminal Header
Marco Diaz
Hands-on Senior Engineering Manager track - Payments/Fintech - Mobile - DevEx - AI Tooling
- Technical engineering leader with 10+ years in software and 5+ years in people leadership, focused on scaling customer-critical payments and platform systems.
- Own and operate a multi-tool AI engineering stack across Codex, GitHub Copilot, and Atlassian Rovo for real product delivery.
- Designed and maintain the golden prompts, enablement playbooks, and workflow standards used by teams to adopt AI consistently.
- Translate AI adoption into measurable outcomes, including over 30% productivity improvement and major manual-hour reduction in scientific and engineering workflows.
- Leadership style emphasizes extreme ownership, decentralized execution, and clarity under pressure, inspired by practical frameworks like Leadership Strategy and Tactics.
Delivery Speed: +28%Reliability: -37%Team Health: +22%
quick-proof.sh
Quick Proof
$ scientific_workflow_automation:
~80 hours saved per recurring batch
Enabled Staff Scientists with Codex + Python automation for Mass Spec workflows previously run manually.
$ engineering_productivity:
+30%
Productivity lift from DevEx standards + Codex enablement.
$ payments_products:
One Pay Credit Card, Pay Over Time with One
Led delivery across customer-facing payments journeys.
$ leadership_efficiency:
~35% productivity + contractor reduction
Scaled and optimized team mix at peak scope, saving hundreds of thousands annually in contract spend.
impact.dashboard
Impact Dashboard
Delivery Speed
+28%
Quarter-over-quarter acceleration
Estimated from quarterly cycle-time tracking across mobile + platform delivery programs.
Reliability
-37%
Incident volume reduction
Estimated trend from incident and escalation records after introducing guardrails and observability standards.
Team Health
+22%
Execution confidence trend
Internal team-health signal based on predictability, ownership clarity, and coaching consistency.
AI Adoption
82%
Sustained weekly usage
Tracked through an OPEX scorecard I designed and coded across engineering workflows.
Platform Coverage
91%
Golden-path adoption
Estimated repository adoption of templates, pipeline standards, and quality checks.
leadership.scope
Leadership Scope Growth
Initial EM promotion
Stage 1 - Engineering Manager Scope
4 peer engineers (2 iOS, 2 Android)
Wins
- Established execution rhythm and delivery ownership in mobile payments.
- Built a strong technical baseline for cross-platform payment features.
Outcomes
- Created high-trust operating cadence that enabled rapid expansion.
- Prepared team for higher-complexity, cross-functional programs.
Post major delivery wins
Stage 2 - Senior Manager Expansion
8 FTE + 10 contractors
Wins
- Delivered Walmart EV Charging E2E and Walmart Pay One Way to Pay.
- Led One Pay migration from legacy Capital One flow with business/legal alignment.
Outcomes
- Supported multimillion-dollar payment-flow impact.
- Improved cross-team predictability and reduced release risk.
Peak scope period
Stage 3 - Peak Organization Optimization
10 FTE + 15 contractors (peak), then contractor reduction
Wins
- Set explicit leadership goals tied to velocity and quality.
- Empowered full-time engineers to own more critical implementation paths.
Outcomes
- ~35% productivity improvement across delivery streams.
- Saved hundreds of thousands in annual contract expenditure.
impact.voices
Voice of Impact
Codex CLI + GitLab on active .NET codebase
“Codex became the most effective code assistant in our delivery flow once we integrated it through CLI into the real repo context.”
Senior Engineer, Internal Product Team
- Added unit tests for a class that previously had no test coverage.
- Renamed class and namespace safely in a production codebase.
- Implemented an entire Jira ticket in about 1 hour vs ~2 day estimate.
- Recovered from first-pass failure by adding richer context and codebase constraints.
AI ToolingDevExBackend
Clinical mass spectrometry tooling enablement
“Codex helped translate expert lab know-how into production-grade internal tools without heavy engineering overhead.”
Staff Scientist Partner, Thermo Fisher
- Built 3 internal apps in days with Codex + Python support.
- Reduced one manual collection workflow from ~30 minutes to ~5 minutes.
- Automated review/report preparation that was costing ~15-20 minutes per sample.
- Unlocked an estimated ~60-80 manual hours saved across ~500 recurring samples.
AI ToolingPlatformDevExReliability
leadership.playbook
Leadership Playbook
Execution Cadence
Reliable execution starts with clear operating rhythm and decision quality.
- Weekly operating review linking roadmap, delivery confidence, and risk.
- Monthly architecture checkpoints for cross-team dependencies and tradeoffs.
- Visible KPI scorecard (velocity, reliability, AI adoption, team health).
- Codified delivery ownership map so each stream has explicit decision accountability.
Incident Model
Incidents are run as leadership exercises, not just technical drills.
- Defined severity model, escalation paths, and response ownership.
- Blameless postmortems with concrete remediation and recurrence guardrails.
- Readiness practice across product, engineering, and support stakeholders.
- Rotating incident command model with postmortem governance reviews at leadership level.
Hiring and Coaching
High-performing teams are built through deliberate talent systems.
- Structured interview loops with role-level scorecards and calibration.
- Manager + senior engineer coaching plans tied to measurable growth goals.
- Promotion-readiness framework focused on scope, impact, and influence.
- Calibration checkpoints to align promotions, growth plans, and succession readiness.
experience.log
Experience Timeline
Timeline Mode
Thermo Fisher Scientific
Staff Engineer - Developer Experience
Jan 2026 - Present
Drove developer productivity strategy across CI/CD standards, automation, and platform engineering practices.
LeadershipDevExPlatformImplemented Codex-enabled workflows and playbooks that contributed to over 30% engineering productivity improvement.
AI ToolingDevExLeadershipEstablished reusable golden-path templates for services and pipelines to improve onboarding and consistency.
DevExPlatformBackendStrengthened reliability through release guardrails, automated checks, and clearer operational ownership.
ReliabilityPlatformDevExPartnered with engineering leaders to align platform investments to measurable team outcomes.
LeadershipPlatform
Walmart Global Tech
Senior Engineering Manager II - Payments
Sunnyvale, California
Sep 2022 - Jan 2026
Drove key wins including Walmart EV Charging E2E and Walmart Pay One Way to Pay across EBT, Walmart Cash, Gift Cards, and additional tenders.
LeadershipPaymentsMobileBackendScaled organization scope to 8 FTE + 10 contractors across critical mobile and backend payment programs.
LeadershipPlatformActed as technical lead for One Way to Pay implementations that supported multimillion-dollar revenue impact.
LeadershipPaymentsBackendLed migration from legacy credit-card program flow to One Pay under business and legal constraint alignment.
PaymentsBackendReliabilityAt peak scope led 10 FTE + 15 contractors, improved productivity by ~35%, and reduced contractor dependence to save hundreds of thousands annually.
LeadershipPlatform
Walmart Global Tech
Senior Engineering Manager - Payments
Sunnyvale, California
Mar 2021 - Sep 2022
Promoted from senior IC track into management and led a pod of 4 peers (2 iOS, 2 Android).
LeadershipMobileEstablished execution cadence, engineering standards, and release governance for high-visibility payment workstreams.
LeadershipReliabilityPlatformDrove architecture alignment across mobile and services for scalable wallet and tender orchestration.
PaymentsMobileBackendBuilt cross-functional trust model with product and architecture leaders to accelerate critical program decisions.
LeadershipPlatform
Walmart Global Tech
Senior Mobile Engineer
San Francisco Bay Area
Jun 2018 - Mar 2021
Designed and delivered core grocery app flows across pickup, check-in, checkout, delivery, favorites, search, and payments.
MobilePaymentsFrontendBuilt on a high-scale, multi-tenant commerce platform with Java, Kotlin, React Native, and backend integrations.
MobileBackendReliabilityImplemented analytics instrumentation and observability to improve product decisions and production debugging.
MobileBackendReliabilityStrengthened quality with CI/CD pipelines, test automation, and TDD practices using Jenkins, Maven, TestNG, and Appium.
DevExMobilePlatform
Walmart Labs
Android Engineer (Contract)
Sunnyvale, California
Aug 2017 - Jun 2018
Delivered Android capabilities for Walmart Grocery app flows and payment-adjacent customer journeys.
MobilePaymentsFrontendImplemented production fixes and performance improvements in a large-scale mobile commerce platform.
MobileReliabilityAutomated regression coverage and improved release confidence through mobile test tooling.
DevExMobileReliabilityCollaborated across product, QA, and platform teams to ship on tight timelines.
LeadershipMobile
Hexaware Technologies
Associate System Engineer
Saltillo, Coahuila, Mexico
Mar 2017 - Aug 2017
Contributed to enterprise software implementation and support for client-facing systems.
BackendReliabilityImproved delivery quality through defect triage, issue resolution, and structured handoffs.
ReliabilityPlatformCollaborated with cross-functional stakeholders to align requirements and technical execution.
LeadershipBackendStrengthened foundational engineering practices for scalable software delivery.
PlatformDevEx
G&G Ingenieria E Innovacion Tecnologica
Jr Android Engineer
Queretaro, Mexico
Nov 2013 - Aug 2016
Implemented native Android applications based on client designs with strong deadline discipline.
MobileFrontendSupported QA and automation efforts to improve release stability and product quality.
MobileReliabilityDevExTracked and resolved defects through structured ticket workflows and close team collaboration.
ReliabilityPlatformBuilt core engineering fundamentals that later scaled into leadership and platform ownership roles.
LeadershipMobile
skills.matrix
Skills Matrix
| Level | Mobile | Payments/Fintech | Backend | Frontend | Platform/DevEx | AI Tooling |
|---|---|---|---|---|---|---|
| Expert | Android Architecture | Payment Orchestration / Wallet and Tender Systems | - | - | CI/CD and Golden Paths / Developer Productivity Programs | Codex Enablement |
| Strong | Mobile Platform Reliability / iOS Delivery Collaboration | Risk and Controls | Service Architecture / API and Event Integrations / Distributed Operations | Product Delivery Alignment / UX and Accessibility Reviews | Internal Platform Standards | AI-assisted Engineering Workflows / Prompt and Tooling Strategy |
| Familiar | - | - | - | Design System Partnerships | - | - |
github.activity
GitHub Activity
Recent repositories and contribution blocks, including private-work approximation.
GitHub ProfileRepository activity is temporarily unavailable. Verify GitHub username or wait for API limits to reset.
Contribution blocks based on recent updates and sustained activity pattern.
case-studies.md
Case Studies
Payments at Walmart
One Way to Pay, One Pay transition, and multimethod checkout scale
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Payments at Walmart
One Way to Pay, One Pay transition, and multimethod checkout scale
LeadershipPaymentsMobileBackendReliability
Problem
Walmart needed to launch and evolve modern payment experiences while maintaining reliability, trust, and execution speed.
Constraints
- Large customer scale with strict uptime and performance expectations.
- Cross-functional dependencies across mobile, backend, risk, and product organizations.
- Business and legal constraints during migration from legacy card-program flow to One Pay ecosystem direction.
Approach
- Created clear ownership and operating cadence across teams and technical domains.
- Aligned architecture around resilient payment flows, observability, and graceful failure handling across One Way to Pay.
- Drove iterative launches with disciplined release controls and customer-impact monitoring.
Results
- Delivered major programs including Walmart EV Charging E2E, One Way to Pay, and One Pay migration enablement workstreams.
- Improved delivery confidence through stronger reliability guardrails and incident readiness.
Lessons
- Payments leadership requires both technical rigor and tight cross-team execution alignment.
- Customer trust scales when product velocity and reliability discipline are treated as co-equal goals.
DevEx at Thermo Fisher
Codex adoption and platform standards for engineering velocity
ExpandCollapse
DevEx at Thermo Fisher
Codex adoption and platform standards for engineering velocity
LeadershipDevExAI ToolingPlatformReliability
Problem
Engineering teams needed a consistent, low-friction way to ship quality software faster without increasing operational risk.
Constraints
- Tooling and workflow fragmentation across repositories and teams.
- Need to increase throughput while keeping reliability and governance intact.
- Adoption had to be practical for teams with different maturity levels.
Approach
- Defined standard CI/CD templates and implementation playbooks for common engineering workflows.
- Integrated Codex-assisted patterns for repetitive tasks, documentation, and troubleshooting.
- Introduced adoption support, feedback loops, and measurable outcome tracking for teams.
Results
- Realized more than 30% engineering productivity improvement through DevEx + AI tooling enablement.
- Reduced delivery friction and improved consistency across planning, implementation, and release activities.
Lessons
- Developer experience gains are durable when standards are easy to adopt and clearly measurable.
- AI tooling delivers the most value when embedded into everyday workflows, not treated as side experiments.
AI-enabled Scientific Workflow Automation
Codex + Python enablement with Staff Scientist partners
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AI-enabled Scientific Workflow Automation
Codex + Python enablement with Staff Scientist partners
AI ToolingPlatformDevExReliabilityLeadership
Problem
Mass spectrometry data processing required manual extraction and parsing across SQLite, CSV, TXT, and PDF files, creating delays and avoidable errors.
Constraints
- Regulated workflow expectations with traceability and compliance requirements.
- Domain logic lived with subject-matter experts, not in repeatable tooling.
- Manual cycle was consuming roughly 80 hours per recurring batch.
Approach
- Partnered directly with Staff Scientists to encode lab-domain logic into Codex-assisted Python tooling.
- Implemented automated delta analysis, QC threshold checks, and structured validation steps.
- Automated reporting outputs and operational traceability fields (work order, instrument, operator attribution).
Results
- Moved from ~20 minutes per sample manual handling to near-instant processing flows for key steps.
- Reduced recurring manual effort by approximately 80 hours per batch while improving consistency.
Lessons
- AI adoption scales fastest when enablement is paired with domain experts and measurable outcome tracking.
- Codex value compounds when DevEx provides reusable patterns, guardrails, and coaching.
Privada Reforma App
Single-engineer PWA for apartment complex operations
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Privada Reforma App
Single-engineer PWA for apartment complex operations
LeadershipFrontendBackendPlatformAI Tooling
Problem
The complex needed to replace Residentia with a custom, mobile-first system for daily resident and admin operations.
Constraints
- Built and operated by a single engineer with broad functional scope.
- Needed mobile app behavior through a PWA without native app overhead.
- Required phased rollout for auth/users, QR access, amenities, incidents, and finance/transparency modules.
Approach
- Built the MVP with React 19, TypeScript, Vite, Supabase, and feature-based modular architecture by domain.
- Used ChatGPT and Codex 5.3 to accelerate screen mapping, documentation workflows, and repetitive coding tasks.
- Implemented linting/formatting standards plus Vitest + Testing Library coverage to keep quality high while moving fast.
Results
- Delivered an extensible platform foundation replacing Residentia workflows with QR access, incident, amenities, and finance capabilities.
- Reduced implementation time by leveraging AI-assisted workflows for technical authoring and execution speed.
Lessons
- A well-designed PWA can deliver strong mobile outcomes without heavy native investment in early phases.
- With disciplined AI usage, a single engineer can sustain velocity while preserving engineering quality.
contact.sh
Let's Build the Next Platform Win
Open to Senior Manager and senior leadership conversations where business outcomes, engineering rigor, and team growth are all first-class priorities.