# Merlijn Vos

![Merlijn Vos](/resources/cognition/portraits/merlijn-vos.webp)

User-centric development, AI evaluations, and leadership  
Cognition  
Amsterdam, North Holland, Netherlands

## At Cognition

- Role: Lead Applied Engineer, Evaluations (Engineering)
- Joined: Sep 2025
- How they joined: Directly
- Before Cognition: Co-Founder, Briqs

## Identity
- LinkedIn: https://www.linkedin.com/in/merlijn-vos
- X: @Murderlon
- GitHub: https://github.com/murderlon
- Domain: cognition.ai

## Notes
- LinkedIn post (verbatim): "Working on FrontierCode has been my daily bread and butter for almost a year, covering everything from creating some of the biggest tasks in the set, hiring, guiding, and onboarding Open Source maintainers, to improving the tooling and end-to-end authoring workflow." (https://www.linkedin.com/posts/merlijn-vos_introducing-frontiercode-a-new-coding-eval-activity-7470023635030958080-a6EC?utm_source=social_share_send&utm_medium=member_desktop_web&rcm=ACoAAHCanKIBY5mvNUmuesGnKpUAGt1HDtH6N_c)
- Same LinkedIn post (verbatim): "I'm also grateful to have my own team of leading experts from the Open Source community. We often had deep discussions on correctness versus quality and what mergeability means in the context of this repository and task, taking into account the philosophy of the maintainers of the project.". (https://www.linkedin.com/posts/merlijn-vos_introducing-frontiercode-a-new-coding-eval-activity-7470023635030958080-a6EC?utm_source=social_share_send&utm_medium=member_desktop_web&rcm=ACoAAHCanKIBY5mvNUmuesGnKpUAGt1HDtH6N_c)
- X thread (verbatim): "FrontierCode finally dropped, a coding agents benchmark for the real world. Human-verified through an extensive hardening process, with a new continuous scoring model. Working on it has been my daily bread and butter for almost a year." (https://x.com/Murderlon/status/2064086502335037622)
- Cognition's FrontierCode launch post quotes him verbatim as 'Merlijn Vos, Core Maintainer of uppy (30.8k stars)': "FrontierCode is a milestone for AI models respecting subjective quality in the real world." He was recruited for evals in his capacity as an open-source maintainer. (https://cognition.com/blog/frontier-code)
- FrontierCode 2.0 acknowledgments list him among pod leads (marked *) alongside Claudio Costa (Mattermost), Martin McKeaveney, Tomer Nosrati (Celery) and Cristiam Da Silva. (https://cognition.com/blog/frontier-code-2.0)
- Cognition's SWE-1.6 preview gives 'extra credit' to contractor-team members with outsized contributions to data & tooling: Claudio Costa, Martin McKeaveney, Lance Fuchia, Tomer Nosrati, Merlijn Vos. (https://cognition.com/blog/swe-1-6-preview)
- X (verbatim): "FrontierCode 2.0 is a massive leap in benchmark quality over 1.1, reflecting real-world usage a lot more. Let's see if the vibes confirm it. We desperately need some AI relevance in Europe." (on Mistral's FrontierCode 2.0 result). (https://x.com/Murderlon/status/2116103602674561233)
- Public headline says "User-centric development, AI evaluations, and leadership". (https://www.linkedin.com/in/merlijn-vos)
- Spoke at TechFems Barcelona (hosted by Happy Scribe) on 'Open Source Evolution: from Past to Contribution'; the speaker bio calls him an award-winning Senior Full-Stack Engineer who helps maintain over 400 packages downloaded hundreds of millions of times. (https://www.techbarcelona.com/en/event/tech-talks-on-open-source-software-hosted-by-happy-scribe/)
- • Applied AI Engineering. Deep expertise in AI (coding) evaluations and agentic engineering.

• Knowledgeable across the stack. Familiar and comfortable in building full-stack web apps in all forms 
and sizes, cloud infrastructure, and developer tooling.

• Proactive without boundaries. I’m a good engineer with great habits. I have a passion that drives me to help out and elevate others, and the product, beyond the minimum requirements. I can take ownership from the earliest stages of talking to; this comes from the profile summary and preserves the person's own positioning. (https://www.linkedin.com/in/merlijn-vos)
- Previous roles include Applied Engineer, Evaluations at Cognition; Full Stack Developer at Transloadit; Co-Founder at Briqs; Frontend Developer at Adyen; Frontend Developer at CLEVER°FRANKE; Frontend Developer at De Voorhoede. (https://www.linkedin.com/in/merlijn-vos)
- Education history includes Bachelor of Science - BS, Communication & Multimedia Design, Amsterdam University of Applied Sciences; Minor, Web development, Amsterdam University of Applied Sciences. (https://www.linkedin.com/in/merlijn-vos)
- Location is Amsterdam, North Holland, Netherlands. (https://www.linkedin.com/in/merlijn-vos)

## Experience
- Lead Applied Engineer, Evaluations at Cognition (Jan 2026 - Present): Leading a team within the bigger evaluations initiative at Cognition. 

Covering everything from creating some of the biggest tasks in the set, hiring, guiding, and onboarding people, to improving the tooling and end-to-end authoring workflow.
- Open Source Developer at GitHub (Nov 2018 - Present): Working on Open Source Software on the GitHub platform (not employed by GitHub):

unified
core team member • https://unifiedjs.com
The core team is a collective team responsible for governing all other teams (unified, remark, rehype, retext, redot, mdx, micromark, syntax-tree, vfile)

tus
core team member • https://tus.io
Open protocol for resumable uploads.

uppy
core team member • https://uppy.io
The next open source file uploader for web browsers
- Applied Engineer, Evaluations at Cognition (Sep 2025 - Jan 2026): Working on evaluations and tooling to improve Devin
- Full Stack Developer at Transloadit (Apr 2021 - Jan 2026): • Maintained a globally distributed file progressing API (frontend/backend).

• Defined and actively implemented long-term visions for open source libraries.

• Dealt and prioritized with a constant flow of issues across multiple projects, our community forum, and through customer support.

• Campaigned for quarterly goals and guided the founders in the process to help us pick work that aligns with business interest.

• Spearheaded the effort to collect all concerns of the Uppy documentation website, rewrote most docs based on that, did the visual design for the website, and the development work

• Spearheaded the creation of tus Node.js, a server for resumable uploads.

• Delivered succinct, engaging writing in blog posts, job posts, and docs.
- Co-Founder at Briqs (Sep 2024 - Oct 2025): Building Dime (later renamed to Briqs), an embedded lending service for platforms and marketplaces.

Leading the infrastructure, front-end, and backend of our integrations and AI underwriting engine.
- Frontend Developer at Adyen - Amsterdam, North Holland, Netherlands (Aug 2020 - Mar 2021): • Building the terminal fleet manager, the software that manages all the payment enabled devices in the field for all customers.

• Contributed to the design system components (Vue).

• Part of the hiring process  (interviews, onboarding).
- Frontend Developer at CLEVER°FRANKE - Utrecht, Netherlands (Aug 2018 - Aug 2020): • Pushed the boundaries of data visualization on the web with D3.js.

• Worked on an accessibility critical government pandemic website.

• For the Opus project I eventually transitioned into a temporary Tech Lead role. I focussed on onboarding new developers, steering the technical direction, and eventually the handover of the project to a new internal Warner Music Group team

• Part of the hiring process (interviews, onboarding)
- Frontend Developer at CLEVER°FRANKE - Utrecht, Netherlands (Sep 2017 - Aug 2018): Worked directly with The Things Network, from requirements gathering, to UX research/design, and eventually delivering a storytelling frontend experience.
- Frontend Developer at De Voorhoede - Amsterdam, North Holland, Netherlands (Jan 2016 - Jan 2016): • Worked on Sita’s Drop & Fly, a self-service baggage drop-off with a web UI. The user interface is adaptable to each specific airport with a system to customize styling, texts and available languages.

• Worked on an internal analytics dashboard for NOS.

• Worked on the website and dashboard of Powerpeers.

## Education
- Amsterdam University of Applied Sciences - Bachelor of Science - BS, Communication & Multimedia Design - (Jan 2014 - Jan 2018): At its heart, the degree programme is about gaining mastery of the design process: from understanding the design problem via developing and building the product all the way through to the official launch – and then working on a second version that is a little better still.
- Amsterdam University of Applied Sciences - Minor, Web development - (Jan 2016 - Jan 2017): A half year minor on web development with a focus on progressive enhancement, accessibility, CSS, semantic HTML, and JavaScript. Projects were always provided by companies with real world use cases.

## Sources
- https://www.linkedin.com/in/merlijn-vos
- https://github.com/murderlon
- https://x.com/Murderlon
- https://cognition.com/blog/frontier-code
- https://www.linkedin.com/in/merlijn-vos?miniProfileUrn=urn%3Ali%3Afsd_profile%3AACoAAEJtnAQBKsaaUC8rhO1IWszWtVjDhsXCEIo
- https://cognition.com/blog/frontier-code-2.0
- https://cognition.com/blog/swe-1-6-preview
- https://www.techbarcelona.com/en/event/tech-talks-on-open-source-software-hosted-by-happy-scribe/
- https://www.linkedin.com/posts/merlijn-vos_introducing-frontiercode-a-new-coding-eval-activity-7470023635030958080-a6EC?utm_source=social_share_send&utm_medium=member_desktop_web&rcm=ACoAAHCanKIBY5mvNUmuesGnKpUAGt1HDtH6N_c
- https://x.com/Murderlon/status/2064086502335037622
- https://x.com/Murderlon/status/2064086530495561870
- https://x.com/Murderlon/status/2116103602674561233


Researched with Autumn (https://www.autumn.ai) from public sources. Updated 2026-11-04. Profile: https://www.autumn.ai/resources/cognition/people/merlijn-vos · Everyone at Cognition: https://www.autumn.ai/resources/cognition/people