Hi, I'm Alex, a software engineer in Denmark with a BEng in Software Technology from DTU. Most of my work is C# and .NET: backend services, REST APIs, and enterprise integrations.
Available for new freelance and contract work: .NET and full-stack web applications, REST APIs, enterprise and tax-authority integrations (SKAT, SAF-T, NemHandel/Peppol), Stripe billing, and AI features, remote across the EU on CET. Email alex.batten1234@gmail.com or send a brief through the form on this site. The full CV also answers frequently asked questions about availability, stack, and how to start a project.
Signed contract, first assignment still pending. The agreed scope is the infrastructure behind AI training, evaluation, and deployment pipelines, in Python and TypeScript. Stack: Python, TypeScript.
Building a multi-tenant Danish bookkeeping SaaS across the stack: microservices in ASP.NET Core and EF Core on .NET Aspire and Azure, with OpenAPI/NSwag generated typed clients, and the Next.js client on top. Moved six services onto a shared service base for startup, configuration, health checks, OpenAPI docs, and authorization. Took VAT reporting to SKAT from the 17-field return calculation through to the Next.js screens and SKAT's production gateway. The integration signs its NemVirksomhed (RSU) SOAP calls with WS-Security, using a certificate held in Azure Key Vault. Built the bank reconciliation backend on an open banking feed (Aiia): matches that must sum exactly to the bank line, a reconciliation overview, and an idempotent transaction sync in its own service. Upgraded SAF-T import and export to the 2.1 schema, with tenant isolation and explicit refusal rules, ahead of the 2027 audit-file mandate. Owning Stripe billing end to end: subscriptions and seat logic (proration, credits, plan switching, yearly plans, plan lapses), webhooks, and secret hardening. Built integrations for daily currency rates (Danmarks Nationalbank), CVR company data (Danish Business Authority), and transactional email. Leading e-invoicing over NemHandel and Peppol (OIOUBL, Peppol BIS) and building the service that sends and receives invoices. Wrote the requirements spec, ran the access point provider selection, and clarified the registration model with the Danish Business Authority. Turning the Bookkeeping Act and its executive orders into implementation specs and reviewing the platform's authentication and multi-tenant security. Doing most of the team's in-depth code review. Set up an autonomous AI development agent (an OpenAI dot) that the team assigns GitHub issues to, and developed its operating prompt from a colleague's first draft over seven revisions. The agent is built to hand each change to Codex agents that implement, review, and test it, then open a pull request for human review. Wrote and presented the team's guide to AI-assisted development with Claude Code. Stack: C#, .NET Aspire, ASP.NET Core, Entity Framework, Microservices, Azure, Stripe, Next.js, NemHandel, Peppol, AI Agents.
Writing prompts in natural Danish on topics of general interest and annotating how AI models respond to them. The annotations point out errors in the responses, including errors in their Danish. The finished work becomes training data for large language models. Skills: Data Annotation, Danish Language, Prompt Writing, LLM Training Data.
Evaluating AI model outputs against structured evaluation guidelines and writing the rationale behind every judgment. The work is close reading: checking a response for factual accuracy, sound reasoning, instruction following, and tone, then stating precisely where it holds up and where it breaks down, with evidence. Applying the same standard consistently across a wide range of subject areas so that assessments stay comparable between reviewers. Skills: AI Evaluation, LLM Outputs, Structured Feedback, Technical Writing.
Contributed to advanced AI model development through data annotation, prompt engineering, trajectory refinement, and QA across projects including Clutch Zayu, Maraca Camera, Mechanic Astrologer, and Meter Pavilion (OpenClaw). Crafted system prompts defining model behavior and constraints, and designed single and multi-turn conversational and agentic datasets spanning 50+ risk categories including bias, misinformation, privacy, and safety. Built autonomous agent trajectories exercising skill discovery, memory, long-horizon context, and native tools (cron, sub-agent delegation). Served as both author and reviewer on Mechanic Astrologer. Skills: AI/ML, Prompt Engineering, Agentic AI, Data Annotation.
Developed REST APIs with auth, rate limiting, and monitoring. Built fullstack web apps with Angular, .NET, and Bootstrap, including JWT auth, real-time dashboards, and automated reporting. Migrated an in-house ERP's time representation from quarter hours to minutes across every display, estimate and report field, then rebuilt the billing review on top of it so a task worked by employees from more than one group billed under each of those groups instead of one. Validated the rebuilt invoicing screen by reconciling a full month of billing data against what had actually been invoiced.
Fullstack application bridging two enterprise platforms, transferring and reviewing time registrations from Accelo (PSA) into Microsoft Business Central (ERP). Custom review UI, MSSQL data model, multi-tenant authentication via Microsoft Entra ID, containerized with Docker in a Jenkins CI/CD pipeline, with unit and Selenium integration tests.
Custom API for ISTOBAL (car wash manufacturer) serving operational data to Uno X (Nordic fuel station chain), with token-based authentication and rate limiting with automated email alerts.
Extended a customer monitoring portal with automated SMS notifications triggered by medicine cooler temperature deviations across a sensor network. Added an adjustable pre-alarm tier that warns by SMS and email without raising an incident, with suppression logic so a sensor sitting outside its threshold does not re-notify on every check. Built as a multi-tenant module, each customer with their own sensor configuration and alert thresholds.
Built the initial web application for a body-scan clinic's internal portal, from an empty repository to a working authenticated application in eight working days: project scaffold, Dockerfile, DNS record, SSL certificate, MySQL schema, Entity Framework contexts, JWT login, salted password hashing, role-gated pages, and password reset from an email link.
Real-time dashboards deployed on Raspberry Pis for office TV screens, monitoring time registrations and cron job health.
Integrated the EU VIES API for VAT number validation and the Danish National Bank API for currency exchange rates into a VAT compliance platform.
A plug-and-play AI safety library for .NET, shipped as a NuGet package (Invarix.Guard). Covers prompt injection, PII, and content safety so apps can add guardrails in a few lines of code. Website: invarix.dk. NuGet: nuget.org/packages/Invarix.Guard.
A free .NET library (Invarix.Guard.Evidence), licensed under Elastic License 2.0, that records AI decisions as an append-only audit trail. Each decision is stored as a CloudEvents event keyed on SHA-256 hashes rather than the prompt text. Batches are sealed into an RFC 6962 Merkle tree and signed with the customer's own Ed25519 key, so an auditor can prove no record changed after sealing using standard Certificate Transparency tooling. Includes retention with legal holds, signed deletion certificates, and a streaming export endpoint. Runs fully in process with no outbound calls. Website: invarix.dk. NuGet: nuget.org/packages/Invarix.Guard.Evidence.
A deterministic action firewall for AI agents, shipped as a NuGet package (Invarix.Gate). It sits in front of an agent's tool calls and evaluates each one against a policy before it runs, returning allow, warn, escalate, deny, or terminate. Ten detectors cover destructive SQL, shell commands, git history rewrites, cloud teardown, credential egress, and runaway loops, each grounded in a dated public incident. Matching is pure CPU pattern work with no model call, so a verdict lands in a median of 57 µs and is deterministic under a given policy. Policy is authored in YAML or fluent C#, attaches through Microsoft.Extensions.AI and Microsoft Agent Framework, and reports the surfaces it cannot see rather than rendering a clean run. Ships with a 194 scenario policy corpus where roughly half the cases assert a detector stays quiet. Website: invarix.dk. NuGet: nuget.org/packages/Invarix.Gate.
A concept app for generating customizable guided meditations using AI-driven text-to-speech layered with Hemi-Sync binaural beats, built in React Native for iOS and Android.
An audio distortion plugin with bitcrushing built with the JUCE framework (C++), compatible with most DAWs as a VST.
Unfinished ideas, and things I wish someone had written down before I needed them. Notes are short and about one thing. Posts are longer. Some of it is meant for you to take and build. Nothing published yet.
Languages: C#, C++, Java, TypeScript, JavaScript, Kotlin, SQL.
Frameworks & Libraries: ASP.NET Core, Entity Framework, Angular, .NET, .NET Aspire, Next.js, React Native, Bootstrap, JUCE.
Concepts & Practices: REST APIs, System Design, Distributed Systems, Agile/Scrum, CI/CD, JWT Auth, Docker.
Other: Git, Claude Code, ERP Systems, Multi-tenant SaaS, SAF-T, Audio Engineering.
Electives in Computer Graphics, Rendering, C++ Programming, and Engineering Economics. Bachelor's project: an integration between two ERP systems built from scratch. GPA: 7.62 (Danish 7-point scale).
Wrote about Alex Batten’s work at Simple Agency Group. View the post on LinkedIn.
Endorsed Alex Batten for C#, .NET Framework, and Entity Framework (EF) Core.
Available for new freelance and contract work. Email alex.batten1234@gmail.com or send a brief through the request form on this site. The work I take is .NET and full-stack web applications, REST APIs, enterprise and tax-authority integrations (SKAT, SAF-T, NemHandel/Peppol), Stripe billing, and AI features, remote across the EU on CET. Project requests get a reply within a couple of days.
Email: alex.batten1234@gmail.com. GitHub: github.com/AlexBatten. LinkedIn: Alex Batten. Live chat is also available on this site.
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