Senior Java Software Engineer

Build and improve real-world Java desktop software in a small, influential engineering team where your technical decisions, ideas, and leadership will genuinely matter. Hands-on Java desktop software role focused on Swing-based commercial applications - not web development. About Us Semantics 21 is a multi-award-winning UK software company developing specialist desktop software used internationally within public safety and investigative environments. Our technology helps organisations process and review digital evidence more effectively, supporting work that can have genuine real-world impact in areas including child protection and public safety.

We are growing our engineering team and are looking for a Senior Java Software Engineer to help develop large-scale desktop applications used operationally by organisations internationally. Despite the sensitive environments our software supports, development staff are never exposed to illegal or disturbing material as part of their role.

The Role This is a hands-on software engineering role focused on long-term desktop application development - not web development. You will work across both existing and new applications, contributing to software used daily in real operational environments where reliability, usability, and performance genuinely matter. This role may suit an experienced developer already operating at senior level, or a strong Java developer ready to step into greater technical ownership, mentoring, and long-term product influence.

This role is ideal for someone who enjoys building real software products, solving practical engineering problems, and contributing ideas within a smaller technical team where your voice and technical direction genuinely matter. We are looking for a Senior Java Software Engineer, or a strong Java developer ready to step into senior-level responsibility, to help develop and improve large-scale desktop applications used operationally by organisations internationally.

You will be involved in:
Desktop application development using Java and Swing, with some JavaFX where appropriate Improving and maintaining large commercial codebases Performance optimisation and troubleshooting Designing intuitive desktop user interfaces Database integration using technologies such as MySQL and SQLite File processing, reporting, and data handling Contributing ideas, innovation, and long-term technical improvements across the wider platform Helping guide development standards, architecture decisions, and future technical direction Supporting, mentoring, and where appropriate supervising other developers as the team grows.

We use modern development tooling and actively support sensible use of AI-assisted development tools, such as Codex, where they improve productivity, code understanding, testing, or development workflow. Why Join Us /

What We Offer We are a smaller engineering team where developers are encouraged to contribute ideas, improvements, and innovation - not simply complete assigned tasks. Developers work directly with the CEO within a flat management structure. This gives the development team direct access to someone with hands-on software development, architecture, customer, and investigator experience. Your input will directly influence products, workflows, technical direction, and long-term development decisions across the company.

This is not an environment where developers are treated as interchangeable resources or isolated from decision-making. Your ideas will be heard, challenged, and where appropriate, implemented. This role suits developers who enjoy building real, long-term software products rather than short-lived web, marketing, or internal dashboard projects.

What Were Looking For We are ideally looking for someone with:
Strong commercial Java development experience Experience developing desktop applications using Swing and/or JavaFX Strong understanding of Core Java and object-oriented programming Experience working within larger or long-term codebases Good debugging, analytical, and problem-solving skills Ability to work independently and take ownership of technical challenges Ability to think beyond individual tickets and contribute to longer-term product improvement Strong written and verbal English communication skills

Experience with any of the following would also be beneficial:
Multithreading/concurrency MySQL or SQLite Jasper Reports Git File parsing and processing AI-assisted development workflows Strong personal projects, Git Hub work, or demonstrable practical coding ability are valued more highly than formal qualifications alone. Please include links to previous work, Git Hub, portfolio projects, screenshots, or other examples in your CV or application where available. Working Environment Based from our Stafford (ST18) office This is primarily an office-based role at our Stafford office.

Hybrid working may be considered by exception depending on experience, role fit, and business needs. Shortlisted…