JSONPath Tester: Query JSON with a Vanilla JS Engine — No Libraries

#javascript #webdev #devtools #json

JSONPath is to JSON what XPath is to XML. I built a live JSONPath tester with a full engine written in vanilla JS — no external libraries, runs entirely in your browser.

Try it

JSONPath Tester — DevNestio

Supported syntax

Syntax	Description
`$`	Root
`.key`	Child property
`..key`	Recursive descent
`[n]`	Array index
`[-n]`	Negative index from end
`[*]`	Wildcard
`[a,b]`	Union
`[a:b]`	Slice
`[?(@.key)]`	Existence filter
`[?(@.key op val)]`	Comparison filter

How the engine works

Two-phase: tokenize then query.

Tokenize splits $.store.book[0].author into ['store', 'book', '[0]', 'author'].

The query function recursively consumes tokens:

.. (recursive descent): evaluate here AND recurse into all children
[*]: iterate all array items or object keys
[a:b]: slice with optional step
[?(expr)]: filter with comparison operators

Filter expression parsing

Filter conditions like [?(@.price < 10)] are parsed with regex, then the right-hand side is coerced to number or string as needed before comparison.