Senior Backend Audits and Hardening Engineer (CONTRACT)

Fixier audits and hardens apps before they break in production. We find the reliability, performance and security gaps behind outages, billing spikes and data leaks, then fix them. When a client needs it, we also build new products from scratch.

The role

You work on live client apps. You audit the architecture, set up staging environments, find what will fail at scale, fix it and document it. This is a freelance, remote, project based engagement.

What you will do

• Audit client backends for reliability, performance, security and cost risks
• Fix production issues such as slow queries, broken auth, unbounded API calls and data exposure
• Redesign backend architecture to handle scale
• Set up and review hosting, deployments, CI/CD, environments and monitoring
• Run traffic simulations, load tests and QA, then report the results
• Test AI features: RAG evaluation, prompt injection, jailbreaks and guardrails
• Write clear audit reports and fix notes for non technical founders
• Build new backend services on from scratch projects

Must have

• 2+ years of backend architecture experience (APIs, databases, auth, queues, caching)
• Past freelance experience with delivery to real clients
• Hosting and deployment experience (cloud, containers, CI/CD, rollbacks)
• Experience with traffic simulation, load testing and QA
• SQL and NoSQL databases, REST APIs, Git
• AI harnessing experience: LLM integration, RAG pipelines, evaluations, jailbreak testing
• Clear written communication and the ability to work independently

Bonus

• PROVEN Software audit or code review experience
• Security knowledge (OWASP, secrets handling, access control)
• Incident response and postmortems
• Cloud and AI API cost optimisation
• Experience with AI generated codebases (Cursor, Lovable, Bolt, v0)

Stack

We are stack agnostic. Strong fundamentals matter more than a specific framework.

Engagement

• Type: Freelance contract, fully remote
• Pay: Hourly or per project rate
• Hours and duration: Reoccurring projects

How to apply

• Send your CV or portfolio, two past freelance projects, and one production issue you fixed (what broke, how you found it, what you changed) to aakshar@fixier.co.
• Follow us on Linkedin (Optional but prefferd)