I'd like to see the original NumberFormatException preserved. Could you update the syntaxError method to take an optional Throwable and pass that as the causedBy in the generated JSONException?

Good idea. Updated the pull request.

The error will now look something like this:

Exception in thread "main" org.json.JSONException: Illegal escape. at 9 [character 10 line 1]
at org.json.JSONTokener.syntaxError(JSONTokener.java:448)
at org.json.JSONTokener.nextString(JSONTokener.java:284)
at org.json.JSONTokener.nextValue(JSONTokener.java:365)
at org.json.JSONObject.(JSONObject.java:206)
at org.json.JSONObject.(JSONObject.java:319)
at fix.JSONFix.main(JSONFix.java:8)
Caused by: java.lang.NumberFormatException: For input string: "rl":"
at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
at java.lang.Integer.parseInt(Integer.java:580)
at org.json.JSONTokener.nextString(JSONTokener.java:282)
... 4 more

Looks reasonable. Let me know if you are planning on updating the unit tests.

I didn't see any tests in the repo, so it wasn't clear to me where to add it. I will be happy to add a regression test for this. Is that in a separate repo?

Yeah, they are kept in a separate project: https://github.com/stleary/JSON-Java-unit-test

Thanks. Pull request created for a simple regression test that check that the right type of exception is thrown.

Thank you, will review this evening, if everything seems OK will open a pull request. We generally leave PRs open for about 3 days for comment before merging.

What problem does this code solve?
JSONTokener.nextString() JavaDocs state that JSONExceptions are thrown, but NumberFormatExceptions may also be thrown.

Changes to the API?
No.

Will this require a new release?
This change will be rolled into the next release, which is expected in June 2016 timeframe.

Should the documentation be updated?
No, this brings the code in line with the documentation.

Change to unit tests?
A new unit test is added, which will only succeed with the code change. See stleary/JSON-Java-unit-test#49