Sr. Full-Stack Software Engineer

Jobgether; Spain; Remote; EUR 50,000 - 80,000; Full time

Benefits offered by this job

Flexible schedule

Fully remote opportunity

Part-time commitment

Output-based earnings

Fast onboarding

Job summary

Jobgether is seeking a Sr. Full-Stack Software Engineer for a fully remote contractor role based in Spain. You will work on an AI training project, tackling cross-language coding tasks and multi-language architectures.

The role emphasizes independent contribution, fast onboarding, and flexible hours around about 15 hours per week. You’ll develop across front-end and back-end systems, review AI-generated code, and ensure performance, security, and maintainability.

Qualifications

• Production-ready full-stack experience across web applications.
• Hands-on front-end and back-end proficiency in multiple languages.
• Strong understanding of APIs, state management, databases, and integrations.
• Ability to navigate unfamiliar codebases and evaluate architectures.
• Excellent debugging and analytical problem-solving skills.
• Available to contribute ~15 hours per week with flexible days.

Responsibilities

• Develop, modify, and debug front-end and back-end application components.
• Build user-facing features with supporting services and data models.
• Trace requests and data flows across browsers, APIs, and databases.
• Explore unfamiliar codebases and assess system interactions.
• Diagnose issues in authentication, persistence, networking, and deployment.
• Evaluate, improve, and validate code across languages.
• Review AI-generated solutions for quality, performance, and security.
• Translate complete coding implementations between languages as needed.
• Meet weekly task submission requirements and adhere to specs.

Skills

Full-stack development

Front-end & back-end

API integration

Debugging

Cross-language

Job description

This position is listed on behalf of a partner company, who manages all applications and next steps. Our partner is looking for a Sr. Full-Stack Software Engineer based in Spain.

Join an AI training project where your full-stack engineering expertise will help improve the quality, reliability, and performance of advanced AI-generated software solutions. You will work on challenging development tasks involving application architecture, technical problem-solving, debugging, code evaluation, and cross-language implementation. The role spans both front-end and back-end systems, requiring you to understand and contribute to complete software applications. You will investigate unfamiliar codebases, build and validate solutions, and assess code for correctness, security, and maintainability. This is a fully remote contractor opportunity offering flexible working hours and approximately 15 hours of work per week. It is particularly suited to experienced engineers who enjoy solving complex technical challenges and can contribute independently.

Accountabilities

You will contribute to a range of software engineering and AI training activities, developing, reviewing, and validating challenging technical tasks across the application stack. Your responsibilities will include:

• Develop, modify, and debug front-end and back-end application components.

• Build user-facing features alongside the services, APIs, and data models that support them.

• Trace requests and data flows across browsers, front-end applications, APIs, backend services, databases, and external integrations.

• Explore unfamiliar code repositories, understand existing architectures, and identify how different system components interact.

• Diagnose and resolve technical issues involving application state, API contracts, authentication, data persistence, networking, and deployment.

• Evaluate, improve, and validate code written in multiple programming languages.

• Review AI-generated software solutions for correctness, completeness, performance, security, and maintainability.

• Create, solve, review, and validate complex software engineering tasks, including translating complete coding implementations from one programming language to another.

• Meet the project's minimum weekly task submission requirements and deliver work that complies with established specifications.

Requirements

The ideal candidate is an experienced full-stack engineer with strong practical knowledge of production applications and the ability to work confidently across multiple technologies. You should be comfortable navigating unfamiliar systems, solving complex problems, and evaluating software quality. Required qualifications include:

• Strong professional experience developing and maintaining production-ready full-stack applications.

• Substantial hands‑on experience in both front-end and back-end engineering.

• Production experience working with multiple programming languages.

• Strong understanding of browser-based applications, APIs, application state management, databases, and service integrations.

• Experience understanding, evaluating, and contributing to the architecture of complete software systems.

• Ability to navigate unfamiliar codebases and quickly understand existing application structures.

• Excellent debugging, analytical thinking, and technical problem-solving skills.

• Ability to assess code quality and identify issues related to functionality, performance, security, and maintainability.

• Strong attention to detail and the ability to deliver accurate, well‑validated technical work independently.

• Availability to contribute approximately 15 hours per week, with the flexibility to choose working days and hours.

Benefits

• Competitive compensation: Attractive and competitive package, with payment based on completed tasks that meet project specifications.

• Output-based earnings: Compensation reflects accepted task submissions rather than a fixed hourly rate. Completion time may vary depending on your experience and workflow.

• Flexible schedule: Choose your working hours and days, including weekends, provided there is ongoing project activity.

• Fully remote opportunity: Work from anywhere, with no fixed office location.

• Part‑time commitment: Approximately 15 hours per week, offering flexibility alongside other professional commitments.

• Fast onboarding and start: The project typically fills positions within 48 hours, with selected candidates expected to begin their first tasks within 24–48 hours after completing onboarding.

• Technical development: Work on challenging software engineering problems involving multiple programming languages, system architecture, debugging, and AI‑generated code evaluation.

How Jobgether works:

We use an AI-powered matching process to ensure your application is reviewed quickly, objectively, and fairly against the role's core requirements. Our system identifies the top-fitted candidates, and this shortlist is then shared directly with the hiring company. The final decision and next steps (interviews, assessments) are managed by their internal team.

We appreciate your interest and wish you the best!

Data Privacy Notice: By submitting your application, you acknowledge that Jobgether will process your personal data to evaluate your candidacy and share relevant information with the hiring employer. This processing is based on legitimate interest and pre‑contractual measures under applicable data protection laws (including GDPR). You may exercise your rights (access, rectification, erasure, objection) at any time.

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