2021 Developer Report: The Fastest-Growing Programming Languages In Tech

5 minutes

As the tech sector bounces back with force, it’s an ideal time to look at industry trends during Q3 2021 among the developer community, using SlashData's 21st State of the Developer Nation Report as a guide. What are the most popular programming languages, what languages are growing the fastest and what sectors are hiring specific skills, according to 19,000 surveyed developers across 160 countries? All this and more, in our special round-up.JavaScript popularity continues to soar"The report showed that over 2.5 million developers joined the JavaScript community in the previous 6 months..."Machine Learning jobs & more propels Python forwardThe fastest-growing language of the past 24 months is…The state of Machine Learning and Data Science workflowWhat would make a developer leave their current role?"For just under a third of participants, career advancement and expanding their knowledge or skills are important..."
An exciting time to be in tech

So, what were the key findings of the 21st edition of the State of the Developer Nation Report run by the Developer Nation community and independent analyst firm SlashData, exploring software developer trends including languages, tools, APIs, apps and technology sectors? 

The report also gauged how long developers were in their current role and what would most likely be the reason for them to consider a move, which makes for interesting reading in such a competitive market for talent.

 JavaScript has, after all, been the world's most-used language for several years now, and this hasn’t changed. The language’s continued popularity in web and back-end applications means it still has the crown of the most popular programming language by a significant margin in Q3 2021. The report showed that over 2.5 million developers joined the JavaScript community in the previous 6 months to the report’s release, and 16.4 million developers use it globally.​

 Even in software sectors where JavaScript is not among developers’ top choices, such as data science or embedded development, a fourth of individuals still said they used it in projects.

Note: data for JavaScript also included language derivatives TypeScript and CoffeeScript.

Our work filling JavaScript developer jobs up until Q3 2021 indicates continuous demand for individuals with JavaScript skills, in comparison with 2019.

 The market continues to be hungry for Python developers. The boom in Python uptake leaves the language second in the league table of most popular languages after JavaScript, and one of the fastest-growing.

As many as 2.3 million are reported to have joined the Python developer community in the past 12 months, which totals an approximate growth of 25%. According to SlashData, the language is now used by some 11.3 million coders, primarily within data science and Machine Learning and Internet of Things (IoT) applications – with over 70% of ML developers and data scientists reporting they use Python(and 17% stating they use R).

Our work with clients to recruit for Python developer jobs shows significant growth compared to 2019, with more roles in Python filled in 2021 from Q1 to Q3 than the whole of 2019 alone.

The report states Python has overtaken Java, which is still very widely used (by approximately 9.6 developers) and a go-to for mobile and desktop apps. As tech recruiters, we are still finding Java jobs to be in high demand among our clients, which was still found to be the go-to for mobile and desktop apps in the report.

“The rise of data science and machine learning is a clear factor in Python's popularity. More than 70% of ML developers and data scientists report using Python. For perspective, only 17% use R, the other language often associated with data science,” states SlashData.

The other most popular languages included C/C++ at 7.5 million developers, PHO at 7.3 million and C# at 7.1 million, with web and backend favourite, PHP charting the fastest growth out of the three – growing by approximately 1 million developers in 2021 (up until Q3), with C# acquiring just over half that in the same period.


One language that has steadily continued to grow over the past 2 years has been the open-source programming language, Rust.

It’s used mostly in embedded software and ‘bare metal’ development, as well as AR and VR development, growing faster than any other language in this period – almost tripling in size from just 0.4M developers in Q3 2019 to 1.1M.

The SlashData report states that Rust has “formed a very strong community of developers who care about performance, memory safety, and security.”

In our tech recruitment, we are seeing Rust grow in popularity at an exponential rate too, with over five times the increase in Rust Engineer and Rust Developer jobs in 2021 up until Q3, compared with the whole of 2019.


Kotlin developers are reportedly in high demand too, with the language highlighted as a “rising star,” with SlashData stating that its audience has roughly doubled in three years (from 1.5M developers in Q2 2018 to nearly 3 million in Q3 2021).

 SlashData’s report furthermore provides interesting insight into how individuals are working in data science and machine learning roles as working models continue to become more complex.

 It found that only one in ten DS/ML developers are involved end-to-end in the DS/ML workflow and end-to-end involvement is decreasing. Excluding these generalists, around two-thirds of the remaining DS/ML developers are involved in three or fewer distinct stages of the DS/ML workflow, which represents a longer-term trend towards specialisation in data science and machine learning. “As working practices mature and technical complexity increases, developers have to specialise in order to stay competitive,” states the report.

The report stated data exploration and analysis, model development, and visualisation/presentation are currently forming the bedrock of DS/ML projects and that the workflow is becoming siloed. Developers involved in a particular stage, such as data ingestion, are also often involved in adjacent stages, such as data and feature engineering, but are often less likely to stray further upstream.

Read the full Machine Learning & Data Science report (from p30-36).

In terms of experience, in the majority of stages in the DS/ML workflow, developers have a fairly similar experience profile according to SlashData. Developers involved in model health and lifecycle management and overall project management/specifications, however, tend to be more experienced: 48% of DS/ML developers involved in overall project management/specifications have three to ten years of experience (compared to just 31% of developers involved in any other stage). This rises to 61% for those involved in the model health and lifecycle management stage, as these stages require a distinct skillset.

“For the overall project management and specifications, a generalist skillset and a high-level view are advantageous, allowing these developers to marry business needs with technical requirements for the bigger picture. On the other hand, model health and lifecycle management instead require specialist knowledge,” states the report.

 With tech talent extremely sought-after and lots of movement in the current market, it’s interesting to see developers’ insight into what would make them leave for a new role.

For half of developers, better pay would seal the deal and a better financial package would make them leave their current position.

 How can companies retain talent outside of pay incentive? For just under a third of participants, career advancement (31%) and expanding their knowledge or skills (31%) are important, with advanced and taking on more challenging work most valued among developers with 3-5 years’ experience.

Outside the top three reasons to move roles, was the ability to work remotely (22%) and an attractive company culture (20%), which obviously are significant factors that contribute to employee health and wellbeing.

SlashData found that experienced developers were frequently the most content in their roles and around one in six with over 16 years plus experience said there were no external factors that could make them want to change roles.

“We see much smaller changes with experience for benefits, company culture, and physical working environments as drivers for a change in employer,” states the report. “Developers at all experience levels have similar views on their importance. Interestingly, remote working isn’t so important to early-career developers - many developers at this stage of their careers value the close contact with colleagues.”

 In summary, the market is demonstrating healthy growth across many languages, with JavaScript, Python and Java leading the way.

It’s important to note that all these figures from SlashData’s report are approximate as measuring the adoption of a language completely accurately is quite a challenge. Its figures are based on two pieces of data: the organisation's own estimate of the number of software developers worldwide (which it puts at 26.8 million), as well as its bi-yearly surveys, which reach “tens of thousands of developers every six months.”

Overall, the positive growth in the market is what we’ve seen mirrored in demand for tech talent and we’re delighted to be partnering on many developer jobs across a variety of markets and be part of the industry’s wider bounce back.

Read our 6 takeaways from working in tech recruitment in 2021 for more insight into how we’ve found the year so far.