Query String to JSON

Q: What happens when the same key appears more than once?

It becomes an array, because that is what the sender meant. A query string like tag=a&tag=b is the standard way to express a list, and every server-side framework reads it as one. A converter that keeps only the last value silently discards data, which is the most common bug in hand-written query string parsing. You can force every key to an array if your consumer always expects one, which avoids code that has to check whether it received a string or a list.

Q: Why do some keys have brackets in them?

Because PHP and Rails invented a convention for nesting that the URL specification never defined. A key written as user[name] means a name field inside a user object to those frameworks, and means a key literally called user[name] to everyone else. This tool understands the bracket convention and can expand it into real nesting, but it is off by default — reading it when the sender did not intend it invents a structure that does not match what the server actually received.

Q: Is a plus sign a space or a plus?

It depends where it appears, which is why this catches people out. In the query portion of a URL a plus is the historic encoding for a space, so a+b means a b. In a path segment it is a literal plus. A genuine plus in a query value has to be written as %2B. So a search for C++ arrives as C%2B%2B, and if your decoded output shows a C followed by two spaces, something encoded it wrongly upstream.

Q: Does it handle a full URL or just the query part?

Either. Paste a whole URL and everything before the question mark is ignored, so you can copy straight from the address bar without trimming it first. A fragment after a hash is also dropped, because it never reaches the server — which is worth knowing in itself, since it means anything after a hash is invisible to your backend and absent from your server logs.

Q: What about a key with no value?

A bare key becomes an empty string rather than null or true, because that is what a server actually sees. Frameworks differ on how they present it — some give an empty string, some a boolean, some treat mere presence as truthy — so the tool reports the raw truth and leaves the interpretation to you. A key written with an equals sign and nothing after it is the same thing and produces the same result.

Q: Can it go the other way and build a query string?

Yes. Give it JSON and it produces a properly encoded query string, with arrays expanded into repeated keys and every value percent-encoded. That direction is where hand-rolling goes wrong most often, because it is easy to forget that an ampersand or a hash inside a value must be encoded or it terminates the parameter early — which is exactly how a tracking link ends up losing half its parameters.

Convert a URL query string into JSON and back, with repeated keys becoming arrays and every value decoded properly.

Query string or full URL

Expand bracket nesting (PHP/Rails) Every key as an array Pretty-print

JSON

Conversion runs entirely in your browser. A URL taken from a log or an authenticated session stays on your machine.

What It Does

Paste a query string — or a whole URL, since everything before the question mark is ignored — and get JSON. The part that matters is what happens to a key appearing twice. Something like tag=a&tag=b is the standard way to express a list, and a converter that keeps only the last value silently throws half the data away. Here it becomes an array, which is what every server-side framework does and what the sender meant. Values are percent-decoded and the plus-sign rule is applied correctly, so a genuine plus must have arrived as %2B. It converts back as well, encoding each value so that an ampersand or hash inside one cannot terminate the parameter early.

When to Use It

A tracking or redirect URL has a dozen parameters and you need to see them as readable structured data.
You are debugging why a form submission is not arriving as expected and want to see exactly what the query carried.
An API expects a query string and you have the parameters as JSON.
A URL pulled from a log needs its parameters extracted for analysis.
You want to confirm a value containing an ampersand was encoded properly before sending the link.

Worked Examples

?name=Jane+Doe&role=admin&active=true

The straightforward case. The plus becomes a space because that is the query-string rule, and the values arrive decoded — note that active is the string true rather than a boolean, since a query string carries no types.

?tag=news&tag=sport&tag=tech

The repeated key case, and the reason this tool exists. Three values under one name become an array. A parser keeping only the last would report tech and silently lose the other two.

https://example.com/search?q=C%2B%2B&page=2#results

A full URL. Everything before the question mark is ignored and the fragment after the hash is dropped, because it never reaches the server. The %2B decodes to a real plus, so the search term is C++ rather than a C followed by spaces.

Features

Query string or full URL accepted

Repeated keys collected into arrays

Optional force-array mode for consistent consumers

Bracket-style nesting expanded on request

Correct plus-sign and percent-decoding

Fragment and path stripped automatically

Reverse conversion from JSON to an encoded query string

Keys with no value reported as a server sees them

Parameter count and duplicate detection

Runs entirely in your browser

How to Use

1. Choose a direction — query string to JSON, or JSON to query string. 2. Paste a query string, a whole URL, or your JSON. 3. The result appears immediately, with a note about repeated keys and anything unusual. 4. Turn on bracket nesting only if the sender used the PHP or Rails convention. 5. Copy the result.

Common Mistakes

Keeping only the last value for a repeated key. That is the standard way to send a list, so discarding the rest loses real data with no warning at all.
Treating a plus as a literal plus. In a query string it decodes to a space, so a genuine plus has to be sent as %2B or it arrives as whitespace.
Assuming bracket nesting is standard. It is a PHP and Rails convention rather than part of any URL specification, and reading it when the sender did not intend it invents structure.
Forgetting to encode values when building a query string. An unencoded ampersand or hash inside a value ends the parameter, which is how tracking links quietly lose half their data.
Expecting the fragment to reach your server. Everything after a hash stays in the browser, so it never appears in your backend or your logs.

Frequently Asked Questions

What happens when the same key appears more than once?

Why do some keys have brackets in them?

Is a plus sign a space or a plus?

Does it handle a full URL or just the query part?

What about a key with no value?

Can it go the other way and build a query string?