Parsimony is a web-based development environment for constructing parsers by example — provide examples of correct parses, and Parsimony will attempt to guess syntax rules based on those examples.
Load the online demo by clicking here. Then install the demo projects by opening the Help menu and clicking Install Example Projects.
Two prerequisites: a Java 8 runtime and a recent (2017) version of the Chrome browser.
Download Parsimony for yourself. There's no installation — just a portable, executable jar file.
Execute it from the command line:
java -jar parsimony.jar --serve
Then navigate to the user interface at http://localhost:9254 from Chrome.
Parsimony is open source. It's mostly Clojure and ClojureScript, with a pinch of C++ for taste.