Senior Full Stack Developer (Remote | $50–$100/hr)

Synthires; Spain; Remote; EUR 62,000 - 124,000; Full time

Job summary

Synthires is seeking a Senior Full-Stack Software Engineer on a contractor basis. The role is fully remote worldwide, focusing on AI-driven software development tasks, debugging, and cross-language translation of code.

You will work across frontend and backend systems and review AI-generated solutions. The ideal candidate has hands-on experience in both frontend and backend engineering, with the ability to navigate unfamiliar codebases and contribute to end-to-end architecture and deployment

Qualifications

• Meaningful hands-on experience in both frontend and backend engineering.
• Experience contributing to the architecture of complete software systems.
• Ability to navigate unfamiliar codebases and work across languages.
• Strong debugging, analytical, and technical problem-solving skills.

Responsibilities

• Develop, modify, and debug front-end and back-end components.
• Implement user-facing features and supporting services, APIs, and data models.
• Navigate unfamiliar code repositories and understand existing architecture.
• Diagnose issues related to state, API contracts, authentication, persistence, networking, and deployment.
• Translate code across multiple programming languages.
• Review AI-generated solutions for correctness, performance, security, and maintainability.
• Create and validate challenging software tasks for AI training and evaluation.
• Provide clear technical feedback on implementation quality and design.

Skills

Full-stack

JavaScript/TypeScript

API design

Problem solving

Debugging

Git

Tools

Git

Docker

Job description

Position: Senior Full-Stack Software Engineer

Type: Contractor

Compensation: $50–$100 per hour equivalent (paid per accepted task)

Location: Fully Remote (Worldwide)

About the Opportunity

We are seeking highly skilled Senior Full-Stack Software Engineers to contribute to an AI training project focused on software development, technical problem-solving, debugging, system architecture, and code evaluation.

In this role, you will create, solve, review, and validate challenging software engineering tasks across front-end and back-end systems. You will also work on translating complete coding projects from one programming language to another.

This position requires substantial hands-on experience across the full application stack. Candidates should be comfortable developing and debugging both user-facing applications and the backend services that support them, rather than specializing exclusively in one layer.

Key Responsibilities

• Develop, modify, and debug front-end and back-end application components.
• Implement user-facing features alongside the services, APIs, and data models that support them.
• Navigate unfamiliar code repositories and understand existing application architecture.
• Diagnose and resolve issues involving application state, API contracts, authentication, data persistence, networking, and deployment.
• Evaluate, improve, and translate code across multiple programming languages.
• Review AI-generated solutions for correctness, completeness, performance, security, and maintainability.
• Create and validate technically challenging software engineering tasks for AI training and evaluation.
• Provide clear technical feedback on implementation quality, debugging approaches, and system design.

Required Qualifications

• Meaningful hands-on experience in both front-end and back-end engineering.
• Experience understanding and contributing to the architecture of complete software systems.
• Ability to navigate and work effectively in unfamiliar codebases.
• Strong debugging, analytical, and technical problem-solving skills.

Preferred Qualifications

• Experience working across diverse technology stacks and programming languages.
• Familiarity with modern front-end frameworks, backend architectures, and API development.
• Experience with database design, authentication systems, networking, and external service integrations.
• Ability to assess code quality, performance, security, and maintainability.
• Experience reviewing AI-generated code or contributing to software engineering evaluation projects.

Compensation & Engagement

• Compensation: $50–$100 per hour equivalent, paid per accepted task.
• Work Arrangement: Fully remote, worldwide.
• Time Commitment: Approximately 15 hours per week.
• Weekly Requirement: A minimum number of tasks must be submitted each week.