The Open Source Initiative says it is not just about seeing the source code: the licence must let anyone use, change and pass the software on. UK government goes further and asks its own teams to code in the open.
Pick a licence condition to see how it fits the Open Source Definition. The bar shows how well that condition fits the definition.
Based on the Open Source Initiative's Open Source Definition (version 1.9) and the GNU Project's explanation of copyleft. Not legal advice.
TWO NUMBERS WORTH KNOWING
Small investment, large return.
What the European Commission found about open source and the economy.
€1bn
Invested in open source software by EU companies in 2018
The European Commission's study estimated companies in the EU invested around €1 billion in open source software that year.
INVESTMENT · EC STUDY
€65–95bn
Estimated positive impact on the European economy
The same study predicts a 10% rise in contributions to open source code would add 0.4% to 0.6% to GDP each year.
IMPACT · EC STUDY
Source: European Commission, Commission publishes study on the impact of Open Source on the European economy (2021).
CODING IN THE OPEN
How UK services publish code.
The GOV.UK Service Manual explains how government teams make code open. Its advice is useful for any project.
Open from the start
It is much easier to write code in the open from the beginning than to open an existing repository later, when security checks become costly.
Keep secrets out
Never store secret keys or credentials in the source code. Keep them separately, for example in a secret management system.
Pick a recognised licence
Publish under an Open Source Initiative compatible licence. The Government Digital Service uses the MIT licence.
Look after it
Use Semantic Versioning for updates and be clear about how you will communicate with people who use your code.
AI-generated image, not a photograph of a real person or place.
HOW COPYLEFT WORKS
Copyright, turned around.
AI-generated image, not a photograph of a real person or place.
To copyleft a program, the GNU Project explains, you first state that it is copyrighted, then add distribution terms giving everyone the right to use, modify and redistribute it, but only if those terms stay unchanged.
That keeps the code and its freedoms legally inseparable. GNU contrasts this with public domain software, which anyone could change and redistribute as a proprietary product. The Open Source Definition itself was originally derived from the Debian Free Software Guidelines.
Questions
Questions people ask
Is any software with visible code open source?
No. The Open Source Initiative says open source doesn't just mean access to the source code; the distribution terms must meet all 10 criteria of its definition.
Can open source software be sold?
Yes. The definition says a licence must not stop anyone selling or giving away the software, and must not require a royalty or other fee for that sale.
What is copyleft?
The GNU Project describes it as a way of making a program free and requiring all modified and extended versions to be free as well, using copyright law to do it.
Does the UK government publish its code?
Point 12 of the Service Standard asks teams to make all new source code open and reusable under appropriate licences, with exceptions such as code for unannounced policy.
Is open source code less secure?
The GOV.UK Service Manual says security code does not need to be closed, and that many functions, such as cryptographic algorithms, are better when openly examined while keys stay private.
