Web Developer in Chelmsford

Have you got what it takes to work for an award-winning agency which puts people and the environment first?

Mosaic is excited to announce a rare opportunity for an experienced web developer to join its team with responsibility for building, maintaining and improving websites for clients.

You will take day-to-day technical ownership of our website portfolio, delivering new projects, developing existing sites and keeping our hosting and supporting systems running reliably.

You will combine strong Word Press development skills with practical technical SEO knowledge and confident use of AI-assisted development tools.

Our existing websites use Word Press, Live Canvas and Bootstrap 5.

You will work within that environment while contributing ideas for improving our development processes and selecting appropriate approaches for new projects.

Working closely with our account and content teams, external designers and specialist partners, you will turn client requirements into well-built, accessible and maintainable websites.

Key Responsibilities

Website developement

• Build and improve Word Press websites, landing pages and functionality using PHP, HTML, CSS and Java Script.
• Translate approved designs, components and wireframes into responsive, accessible websites, contributing practical UX improvements throughout development.
• Take projects through scoping, implementation, testing, launch and handover.

Provide realistic estimates, communicate progress and identify dependencies or changes in scope early.

• Review existing websites and codebases to understand their structure, resolve issues and identify worthwhile improvements.
• AI-assisted development and automation
• Use AI-assisted and agentic development tools to improve the efficiency of development, debugging, testing and documentation.
• Structure tasks effectively, provide relevant context and use coding-agent harnesses such as Codex and Claude Code. Experience with Open Code is also welcome.
• Review and validate generated code, test changes thoroughly and ensure the finished work meets requirements for functionality, security, accessibility and maintainability.
• Identify opportunities to automate repetitive tasks and improve internal workflows, while protecting client information, credentials and company data.
• Technical SEO for client retainers and website performance
• Plan and manage ongoing technical SEO work for client retainers, agreeing priorities with account owners and SEO specialists and delivering within each client's agreed scope and allocation.
• Carry out technical checks on an agreed schedule, maintain a prioritised action list and implement and re-test improvements.

Investigate issues affecting website crawling, indexing, performance and usability.

• Implement improvements to redirects, URL structures, internal linking, metadata, canonical tags, sitemaps and structured data where appropriate.
• Review relevant Search Console and website-performance information, investigate technical changes or issues and contribute clear progress updates to client reporting and meetings.
• Work with content colleagues and SEO specialists to assess recommendations, coordinate implementation and escalate matters requiring wider SEO strategy or specialist input.
• Support website launches and migrations with appropriate technical checks, redirect planning and post-launch monitoring.
• Website maintenance, hosting and support
• Maintain client websites and supporting services, including hosting, domains, DNS, SSL, backups and software updates.
• Investigate website problems methodically, communicate their impact and coordinate with hosting providers or specialist support where required.
• Use staging environments, backups, testing and recovery procedures to manage changes safely.
• Maintain clear records of website configurations, licences, access arrangements and maintenance procedures.
• Client communication and collaboration
• Explain technical issues and recommendations clearly to clients and non-technical colleagues.
• Work with account managers to agree priorities across projects and retainers, flag risks and keep delivery aligned with the agreed scope.
• Collaborate with external designers and specialist partners, providing technical input and implementing their work where appropriate.
• Contribute technical input to scoping and new business proposals when required.
• Prepare clear documentation and handovers so that websites and systems can be supported effectively.
• Internal tools and process improvement
• Maintain relevant internal tools, integrations and automations.
• Identify practical improvements to development, reporting and support workflows.
• Document repeatable processes and help colleagues carry out appropriate routine tasks confidently.

Essential skills and experience

• Around five years' relevant commercial web development experience, or equivalent demonstrable experience, with a track record of independently delivering and supporting client websites.
• Strong Word Press and PHP development skills, including experience developing, adapting and troubleshooting themes, plugins and existing implementations.
• Strong front-end skills in HTML, CSS, Java Script and Bootstrap 5, with experience translating designs into responsive, accessible websites.
• Practical experience using AI-assisted development tools on real projects, including planning tasks, reviewing output, debugging and validating completed work.
• Practical technical SEO knowledge, including identifying issues, prioritising ongoing client work, implementing recommendations and checking the effects of changes.
• Website operations and troubleshooting experience, covering hosting, DNS, SSL, backups, security, updates and deployment.
• A disciplined development approach, including version control, testing, documentation and maintainable code.
• Clear communication and independent working, with the ability to manage competing priorities, provide realistic estimates and recognise when specialist input is needed.

Desirable experience

Experience with Live Canvas would be particularly valuable.

Candidates with strong Word Press and Bootstrap 5 skills and the ability to learn the platform are also encouraged to apply.

• 20i hosting and website administration.
• Google Search Console, analytics and technical SEO auditing tools.
• Website migrations, performance optimisation and structured data implementation.
• API integrations, reporting tools and workflow automation.
• UX, wireframing and extending established design systems or component libraries.
• Agency work involving multiple clients, ongoing retainers and support requirements.
• What success looks like

You deliver websites and improvements that meet the agreed brief, work reliably and are straightforward to maintain.

Projects are supported by realistic estimates, clear communication, appropriate testing and safe implementation.

Retainer clients have clear technical SEO priorities, visible progress and records of completed improvements and remaining issues.

Clients and colleagues understand what is happening next.

Your use of AI improves the efficiency of appropriate tasks while maintaining the quality and reliability of the finished work.

Accurate documentation supports effective maintenance and handover.

How to apply

Please send your CV and examples of relevant work to Managing Director Gemma Rawlinson at .

Explain your contribution to selected projects and include an example of using AI to improve a development workflow, including how you reviewed and validated the result.

Please respect client confidentiality and any restrictions on sharing source code.