Programming languages
We use a range of programming languages at GDS because we think using the right tool for the job gives us the best chance of building services that best meet users’ needs. This document does not apply to choosing ‘off the shelf’ software (open source or not).
We focus on using a small number of programming languages for core software development tasks.
This should make it easier for developers to:
- move around the organisation
- develop shared components
- improve their personal development
- master how they operate applications
Frontend development
The Service Manual has information on using client-side JavaScript. For server-side JavaScript we use Node.js.
GDS projects using Node.js include:
- GOV.UK Frontend
- GOV.UK Pay
- GOV.UK PaaS (TypeScript)
- GOV.UK Prototype Kit
- GOV.UK One Login - see repositories in TypeScript and in JavaScript
You can use Node.js to render a web interface for your service. For example, GOV.UK Pay has created thin, client-facing applications that do not store data (although they may retrieve data from an API).
You can use TypeScript when teams think it’s appropriate. For example, the GOV.UK PaaS team uses TypeScript because they are used to working with a statically typed, compiled language, and they think the compilation and static-analysis tooling is better for their workflow. There’s more information about TypeScript on the Node.js page.
Backend development
Our core languages for backend development are:
We’ve chosen these languages because they are successfully used by teams at the moment, and we are confident in how to host and operate applications written in them. You should carry out new development in one of these languages.
Python
You should write new Python projects in Python 3. Python 2 reached end of life in 2020. Python 3 is now well-supported by application frameworks and libraries, and is commonly used in production.
Go
Go is no longer a core backend development language in GDS.
The only Go service currently in production operation is the GOV.UK router, and it is the core language for Cloud Foundry, which GOV.UK PaaS uses, although GOV.UK PaaS is being decommissioned. As such, the knowledge and experience of building and running services in Go is small and decreasing.
Go may be an appropriate language for instances of systems programming, like proxying, routing, and transforming HTTP requests. However you should only write these sorts of components if there is no alternative maintained open source tool available.
Languages we do not use for new projects
We used Scala in the early days of GDS. GOV.UK Licensing is the only remaining application written in Scala but we’ve found it hard to support because of a lack of skills in GDS. Do not use Scala for new projects.
Using other languages
There will be sensible reasons to not follow the above guidance on languages. For example when you’re:
- extending an existing codebase or ecosystem
- scripting in a particular environment
- experimenting during an alpha (with an expectation that it’s replaced by something we have more confidence in for beta)
- working in a very specific or unusual problem domain, like heavy use of WebSockets
The set of languages we’re comfortable supporting will change over time.
If you want to use a new language, talk to your Head of Technology and then create a prototype. If it goes well you can open a pull request to change this document.
If you’re having problems using one of the languages we support, open a pull request to document the issues.