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I'm looking for the program that JSON, SQLite and other projects are using to create the diagrams used for their language syntax, if there is a particular program. All of the diagrams have a similar style, with partially curved connections or arrows indicating flow.
There are some differences, making me wonder if it's a single program or just generic graphing tools used for a particular style.
As you can see by my edits to your question, the kind of syntax diagram you're referring to is also known as a railroad diagram. Wikipedia mentions a few tools under the "External Links" section, including:
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