Web Developer (Intern)

Refinery89; Madrid; On-site; EUR 7,800 - 10,000; Full time

Job summary

Refinery89 is seeking a Web Developer Intern to join the Publisher Success team in Madrid. You will gain hands-on experience with HTML, CSS, and JavaScript while supporting real publisher websites, debugging issues, and learning ad tech integrations.

The role is ideal for students or recent graduates looking to strengthen their web development fundamentals, understand browser tooling, and collaborate with Technical Account Management and developers on practical projects.

Qualifications

• Fluent English required (C1/C2).
• Foundational knowledge of HTML, CSS and JavaScript.
• Understanding of how websites are structured and how frontend technologies interact.
• Experience using browser developer tools to inspect pages or troubleshoot issues.

Responsibilities

• Troubleshoot publisher websites and investigate technical issues using browser tools.
• Work with HTML, CSS and JavaScript on real publisher sites.
• Help monitor websites and identify unusual behavior affecting ads.
• Learn how APIs and ad tech integrations interact with websites.
• Communicate technical findings clearly to publishers in English.

Skills

English (C1/C2)

HTML

CSS

JavaScript

Browser dev tools

Technical curiosity

Problem solving

Communication

Numeracy & data

Reliability

Tools

Git

Job description

About Refinery89

Refinery89 is a Dutch AdTech company headquartered in Madrid, working with premium publishers around the world to optimize their programmatic advertising performance.

Web Developer Intern

Location: Madrid, Spain, Onsite

Team: Publisher Success

Position Type: Internship

English C1/C2 Level: Mandatory

About The Internship

We are looking for a Web Developer Intern to join our Publisher Success team in Madrid.

This internship is designed for a student, recent graduate, or early career candidate who already has a foundation in HTML, CSS, and JavaScript and wants to gain practical professional experience working with websites, technical troubleshooting, data, and advertising technology.

You do not need previous AdTech experience. We will train you on the AdTech side from zero.

During the internship, you will work with real publisher websites, browser developer tools, HTML, CSS, JavaScript, advertising technologies, reporting platforms, and technical diagnostics while receiving support and guidance from experienced members of the team.

The internship is ideal for someone who wants to strengthen their web development fundamentals while gaining experience in technical troubleshooting, website integrations, data, publisher support, and Technical Account Management.

What You Will Do

Website Troubleshooting

• Support the investigation of technical issues affecting publisher websites.
• Use browser developer tools to inspect HTML, CSS, JavaScript, scripts, network activity, and browser errors.
• Help identify issues related to page structure, styling, scripts, advertising tags, or website configuration.
• Reproduce technical problems and investigate their likely cause.
• Review browser console errors and network requests when diagnosing issues.
• Gather the technical information needed before escalating more complex problems to senior team members.

Web Technologies and Integrations

• Work with HTML, CSS, and JavaScript across real publisher websites.
• Help investigate how scripts and third party technologies interact with webpages.
• Support the implementation and validation of advertising related website integrations.
• Review website configurations and identify potential technical issues.
• Learn how APIs, scripts, browser requests, and advertising technologies interact within modern websites.

Publisher Monitoring

• Support the monitoring of publisher websites and identify unusual behavior.
• Perform regular technical health checks.
• Help spot problems affecting advertising performance or website functionality.
• Investigate whether changes on a website may be affecting advertising delivery.
• Learn how different components of a publisher website interact with advertising technology.

Data and Performance

• Learn to interpret advertising metrics such as CPM, RPM, fill rate, impressions, and revenue.
• Identify unusual changes in performance.
• Support investigations into whether an issue may be technical, commercial, or related to traffic.
• Use data to support technical investigations.
• Work with spreadsheets and internal reporting tools.

Technical Communication

• Create clear technical handoffs including screenshots, URLs, browser information, and descriptions of the issue.
• Learn to explain technical findings in simple and understandable language.
• Support communication with publishers in English about technical issues and their resolution.
• Collaborate with Technical Account Managers, developers, advertising specialists, and other internal teams.

What You Will Learn

You will receive structured onboarding and gradually develop knowledge in areas including:

• Advanced website troubleshooting.
• HTML, CSS, and JavaScript in production environments.
• Browser developer tools.
• JavaScript troubleshooting.
• Network requests and browser debugging.
• APIs and web technologies.
• Website integrations.
• Google Ad Manager.
• Prebid.
• SSPs.
• Programmatic advertising.
• Advertising tags and website integrations.
• Publisher monetization.
• Reporting and performance analysis.
• Technical Account Management.

You are not expected to know AdTech before joining.

Must Have Skills

• Fluent professional English (C1/C2).
• Practical knowledge of HTML, CSS, and JavaScript.
• Basic understanding of how websites are structured and how front end technologies interact.
• Some experience using browser developer tools to inspect websites, troubleshoot issues, or understand page behavior.
• Strong technical curiosity.
• Strong problem solving skills.
• Comfort investigating unfamiliar technical problems.
• Clear written and verbal communication.
• Basic numeracy and confidence working with percentages and data.
• Reliability and attention to detail.
• A genuine eagerness to learn.
• The confidence to say, “I don't know yet, but I can investigate.”

Professional Experience Is Not Required.

Preferred Background

• Computer Science.
• Software Engineering.
• Web Development.
• Programming.
• Information Technology.
• Telecommunications.
• Data.
• Engineering.

A formal technical degree is preferred but not required if you can demonstrate practical technical experience.

Internship Eligibility

To participate in this internship, you must be legally eligible to complete an internship in Spain.

Candidates should be enrolled in an educational program or otherwise be eligible to complete an internship agreement through a university, educational institution, or training provider.

Please confirm your internship eligibility when applying.

Things That Will Help You Stand Out

• Experience building or maintaining websites.
• Experience troubleshooting JavaScript errors.
• Familiarity with the browser console.
• Familiarity with network requests.
• Experience working with APIs.
• Basic understanding of HTTP, requests, responses, and browser behavior.
• Exposure to databases.
• Git or GitHub experience.
• Personal web development projects.
• Experience with third party scripts or website integrations.
• Experience helping users solve technical issues.
• Basic spreadsheet skills.
• Spanish language skills are considered a plus but are not required.
• Dutch language skills are considered a plus but are not required.

Who This Internship Is For

This internship could be a strong fit if:

• You enjoy building, inspecting, and understanding websites.
• Something on a website stops working and your instinct is to investigate why.
• You are comfortable opening browser developer tools and inspecting what is happening behind a page.
• You have worked with HTML, CSS, and JavaScript through your studies, personal projects, or previous experience and want to apply that knowledge in a real business environment.
• You see an error in the browser console and want to understand what caused it.
• You enjoy solving technical problems even when you do not immediately know the answer.
• You like working with both technology and people.
• You want to gain professional experience with web technologies without necessarily following a traditional software engineering path.

Important

Although the position is called Web Developer Intern, this is not a traditional software development internship.

You will not spend your internship primarily building applications, developing product features, or working as part of a software engineering product team.

The internship focuses mainly on web technologies, website troubleshooting, technical investigation, integrations, publisher support, advertising technology, performance monitoring, and Technical Account Management.

You will regularly use HTML, CSS, JavaScript, browser developer tools, APIs, and other web technologies to investigate and understand technical issues.

This role is therefore particularly suitable for someone with a web development background who enjoys understanding how websites work, debugging problems, working with integrations, and applying technical knowledge in a client facing business environment.

Interview Process

Our interview process consists of three stages.

• Initial Screening

A short introductory conversation with our recruitment team to understand your background, motivation, English level, internship eligibility, and web development experience.

• Team Interview

A conversation with the Hiring Manager or Technical Account Management team focused on your technical curiosity, web knowledge, problem solving approach, and how you investigate unfamiliar problems.

• Practical Technical Exercise

A practical exercise designed to understand how you approach website related technical problems and learn unfamiliar concepts.

You are not expected to know AdTech before completing the exercise.

We care about your existing web fundamentals, your reasoning process, your willingness to learn, and how you approach technical problems.

Location

This is an onsite internship based in Madrid, Spain.

Join Refinery89. If you are studying or starting your career in web development, already have experience with HTML, CSS, and JavaScript through your studies or personal projects, enjoy understanding how websites work, and want to gain practical professional experience across web technologies, troubleshooting, integrations, data, and AdTech, we would love to hear from you.