JSONPath examples: how to query JSON with RFC 9535 filters, slices and functions

How this is calculated

Before RFC 9535, each library had its own dialect. Some ran script expressions inside filters, some returned single values instead of lists, and a few disagreed on what .. should match. The standard fixed that. A query always returns a list of nodes, and each node has a normalized path, like $['users'][0]['email'], that points at exactly one place. Filters work on a small expression language with comparisons, && || and !, so nothing in a query runs as code. Numbers compare by value. Strings compare by Unicode code points. A comparison between different types, like a number and a string, is simply false instead of an error. The five functions cover the common needs: length() counts characters, items or keys, count() counts the nodes a query finds, match() and search() test a string against a regular expression, and value() turns a one node result into a value you can compare.

Verdict

Use simple paths for known locations and filters for questions. $.orders[0].total reads one value. $.orders[?@.total > 100].id answers a question about every order. Reach for .. only when you don't know how deep a key sits, since it visits every value in the document. Wrap keys with spaces or symbols in brackets and quotes, like $['first name'], and check every query against a real sample before you rely on it in code.