Data from JetBrains’ 2025 Developer Ecosystem Survey reveals that developers’ movement between programming languages is primarily governed by project requirements, although some languages attract users because of the development experience, job opportunities, or performance. Based on 8,837 responses, JetBrains’ analysis presents actual transition paths over one year rather than relying on what developers said they planned to do.
The analysis was prepared by Vladimir Volokhonsky and compares the primary languages participants used 12 months earlier with the languages that had become their primary languages when they answered the survey. Leaving a language does not mean stopping its use entirely; it means that it is no longer the developer’s primary language.
From Intentions to Actual Transitions
In the early years of its survey, JetBrains relied on a question about the languages developers planned to adopt or move to during the following 12 months. However, the company found that plans did not accurately predict actual transitions; wanting to try Rust or move from Java to Kotlin does not necessarily mean carrying out that step.
The company therefore added questions about the primary languages participants had used a year earlier and then compared the current answers with the previous ones. According to the analysis, transitions between languages can follow multiple paths, with transitions among the most widely used languages remaining the largest in number. The path from Python to Java and the reverse direction stood out, while the move from Java to Kotlin ranked third by absolute numbers.
Growth Opportunity Index and the Fastest-Rising Languages
JetBrains introduced what it calls the “Language Promise Index” to track languages’ future migration opportunities, based on the stability of positive or negative transition trends and the number of people interested in learning each language. According to the results, TypeScript, Rust, Python, and Go still have significant growth potential, while Lua is no longer among the leading languages after its growth apparently reached a certain ceiling.
The analysis indicates that TypeScript and Rust were among the most prominent rising languages, while actual growth appeared only for Go among the languages JetBrains expected to grow, such as Python, Go, and Lua. The data also shows that JavaScript, despite being the most widely used language overall, is the primary language for only about 6% of software developers, whereas Java remains more prevalent as a primary language.
Why Do Developers Leave Their Languages?
Project requirements remain the most common reason for moving between languages. However, the reasons for leaving differ from one language to another:
- C: It showed the lowest retention rate in the data; about half of those whose primary language had been C in the previous year moved to another language. About half of them selected “wanting to learn a new language” as the reason, while newer features also appeared as a common reason, which the analysis links to widespread dissatisfaction or a sense that the language is outdated. Nevertheless, C’s presence as a primary language changed little between the two years, rising from 2.0% to 2.1%, and the C sample was very small, with fewer than 100 participants.
- Leaving it is often associated with better opportunities in the job market.
- PHP: Performance and scalability limitations are recurring reasons for moving away from it.
- Java: Developers leaving it tend to move to Python and TypeScript more than to Kotlin, although the move to Kotlin was among the most prominent paths by total number.
JetBrains emphasizes that data for some languages, including Kotlin and PHP, is also based on small samples of fewer than 100 participants, so these results should be treated with caution.
Languages That Attract Developers and Successive Paths
JavaScript appears in both directions: some developers leave it in search of job opportunities, while others move to it for the same reason. A significant part of its growth comes from HTML/CSS developers, forming a successive path from HTML/CSS to JavaScript and then to TypeScript.
Kotlin differs from most paths driven by necessity. According to the analysis, developers move to it in search of a better development experience and more modern language features, not because the project requires it. Its main source of growth is Java, although the flow of developers from Java to Kotlin was weaker than expected, with reverse transitions also occurring.
Go’s appeal is associated with performance and scalability, while Python attracts developers through ecosystem and library support. The data suggests that Python serves as a primary destination for users of most languages, except C users, who preferred Java and C++, and TypeScript users, for whom Java, JavaScript, and C# were the leading destinations.
What Does the New Map Say?
The analysis argues that tracking actual transitions transforms ecosystem data from a static picture of language popularity into a map of developer flows. Some transitions are driven by the need to meet project requirements, while other languages attract developers through performance, the ecosystem, or the development experience.
Java emerges as an important hub, with prominent outflows toward Python and TypeScript, while TypeScript and Rust appear at the forefront of languages with growth opportunities. The data also reveals that a stable share for a language does not necessarily mean its user base is stable; a language may lose developers and gain others at the same time. For Kotlin, its key advantage lies in its ability to attract users, rather than in being a path that projects force developers to take.