Why did `+` turn into a space?

In form-style query strings, `+` is commonly decoded as a space. A literal plus sign should be encoded as `%2B` if you need it preserved.

Why did repeated keys become an array here but not in my app?

Query string parsers make different choices. Some preserve all values, some keep the first, and some keep the last. Compare the tool output with your framework's parser or `URLSearchParams.getAll()` behavior.

Why doesn't nested JSON round-trip cleanly?

Query strings are fundamentally flat. Nested objects and arrays require conventions like bracket notation or custom serialization rules, so the same JSON can produce different valid query strings.

Why are numbers and booleans quoted in JSON output?

Query parameters are text. A query string parser cannot know whether `42` should stay a string or be coerced into a number unless a specific parser adds type inference.

Why does decoding fail on some pasted values?

The input likely contains malformed percent-encoding such as an incomplete `%` escape, or a copied URL fragment that mixes encoded and unencoded characters.

Why do keys like `toString` or `__proto__` work here?

This tool treats query keys literally, so names that happen to match JavaScript object property names are parsed the same as any other key.

Query String Parser / JSON Converter

Parse query strings to JSON or serialize flat JSON objects back to query strings.

Query string input

JSON output

Query parsing follows browser form-style behavior: a leading ? is optional, repeated keys stay repeated, and + decodes to a space.

JSON to query string supports flat objects only. Scalars become one param, arrays of scalars become repeated keys, nested objects are rejected, and null becomes an empty value.