Henry Mercer
Staff Software Engineer at GitHub
United Kingdom
Summary
🤩
Rockstar🎓
Top SchoolHenry Mercer is a Staff Software Engineer at GitHub with a decade of experience building developer-focused security products and tooling. A Cambridge-trained computer scientist specialising in programming language theory and machine learning, he blends rigorous academic foundations with practical engineering across full-stack, backend, and DevOps work. At GitHub he has driven improvements to the CodeQL ecosystem—contributing to the VS Code extension, CLI/package docs, and cross-platform Actions runner automation—helping make code scanning and bundle distribution more reliable and efficient. He has a history of subtle but impactful fixes (e.g., TypeScript compiler property access and nuanced UI/webview bug fixes) and a pattern of improving developer workflows through clearer documentation and automation. Based in the UK, he pairs research-informed thinking with hands-on shipping of secure, production-grade systems.
10 years of coding experience
5 years of employment as a software developer
Master of Engineering - MEng, Computer Science, Distinction, Master of Engineering - MEng, Computer Science, Distinction at University of Cambridge
Stackoverflow
1reputation
0reached
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Github Skills (31)
github-ci10
javascript10
package-management10
scripting10
testing10
typescript10
vscode-extension10
cicd10
codeql10
automation10
script10
typescript-types10
sh10
powershell10
automations10
Programming languages (10)
Github contributions (5)
github/vscode-codeql
Oct 2019 - Oct 2022
An extension for Visual Studio Code that adds rich language support for CodeQL
Role in this project:
Full-stack Developer
Full-stack DeveloperContributions:54 reviews, 138 commits, 79 PRs in 3 years
Contributions summary:Henry primarily contributed to the development and maintenance of the VS Code extension for CodeQL. Their work involved refactoring the archive filesystem provider, modifying distribution settings, and improving error reporting within the extension. They also fixed issues in the user interface and addressed bugs related to query history and webview URI conversions. Furthermore, the user implemented rate limiting for function invocations and CLI update checks.
visual-studio-codevscodevscode-extensionlanguage-supportworks-with-codespaces
github/codeql
Dec 2019 - Jan 2023
CodeQL: the libraries and queries that power security researchers around the world, as well as code scanning in GitHub Advanced Security
Role in this project:Back-end Developer & Documentation Specialist
Back-end Developer & Documentation SpecialistContributions:252 reviews, 381 commits, 200 PRs in 3 years 2 months
Contributions summary:Henry's primary focus was on improving the documentation related to the CodeQL CLI and package management. They added detailed sections on managing CodeQL packs within GitHub Enterprise Server (GHES), including authentication and installation from GHES Container registries. They also updated existing documentation to clarify concepts, correct header formatting, and provide examples of usage. Additionally, the user contributed to internal code enhancements.
github-advanced-securitysecurity-toolsgithub-security-labsecurity-researcherssecurity
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