List to JSON Array

Q: Why is my number staying a string?

If it has a leading zero, that is deliberate. A value like 007 or 01234 is an identifier — a product code, a postcode, a phone number — and turning it into a number destroys the zero permanently, leaving a value that no longer matches anything. Ordinary numbers convert normally. If you want everything to stay a string regardless, turn type detection off; if you want the leading-zero value converted anyway, strip the zero in your source first so the intent is explicit.

Q: What happens to blank lines and stray spaces?

Blank lines are dropped by default, because a trailing newline at the end of a paste would otherwise add an empty string to the end of your array — which is almost never wanted and easy to miss. Leading and trailing spaces on each line are trimmed for the same reason: they usually come from the copy rather than the data. Both are options, so if your values genuinely contain meaningful padding you can keep it.

Q: Can it remove duplicates?

Yes, and it reports how many it removed rather than just handing back a shorter array. That count is usually the thing you actually wanted to know — a list that shrinks by 200 entries tells you something about the source data. Deduplication is case-sensitive by default, which is right for identifiers and codes; switch it to case-insensitive for things like email addresses, where Sam@example.com and sam@example.com are the same person.

Q: Can I produce an array of objects instead of plain values?

Yes. Give a key name and each line becomes an object with that key, so a list of names becomes a list of {"name": "..."} records. That is the shape most APIs and seeders expect for a bulk insert, and building it by hand for a hundred rows is exactly the kind of work worth avoiding. Leave the key blank and you get a plain array of values, which is what you want for an enum, a lookup or a simple parameter list.

Q: How do I get one line per entry rather than pretty-printed?

Turn off pretty-printing for a compact single-line array, which is what you want when the JSON is going into a query parameter, an environment variable or anywhere whitespace costs you. Pretty-printed output is easier to read and to review in a diff, so it is the default. Both represent exactly the same data — the choice is purely about where it is going next.

Q: Is there a limit on how many lines it can handle?

Nothing beyond your machine's memory. Everything runs in your browser, so there is no upload step and no server-side quota, and lists of tens of thousands of lines convert without difficulty. That also means it is safe for data you would not paste into an online service — a customer export, a set of internal hostnames, anything under an agreement. Nothing you paste leaves the page.

Turn a plain list of lines into a JSON array, with sensible type detection and leading-zero codes kept as strings.

Your list (0 lines)

Wrap each line as an object under this key (optional)

Detect numbers, booleans and null Trim whitespace on each line Drop blank lines Remove duplicates Case-sensitive matching Pretty-print

JSON (0 items)

Everything runs in your browser, so a list of internal or customer data never leaves your machine.

What It Does

Paste a list with one entry per line and get a JSON array. The conversion is trivial; the judgement is in what gets typed. Numbers become numbers and true and false become booleans, but a value with a leading zero stays a string — because 007 is a code, not the quantity seven, and converting it destroys the value in a way you cannot undo. Blank lines and stray padding from the copy are dropped by default, since a trailing newline would otherwise put an empty string at the end of your array. Beyond the plain array it can deduplicate and tell you how many it removed, and wrap each line as an object under a key you choose, which is the shape most bulk-insert APIs and database seeders expect.

When to Use It

A column copied out of a spreadsheet needs to become a JSON array for an API request.
You are writing a seeder or a test fixture and have the values as a plain list.
A set of allowed values needs to go into a configuration file as an array.
You need an array of objects for a bulk insert and have one field per line.
You want to know how many distinct values a list actually contains before using it.

Worked Examples

apple
banana
cherry

The simplest case — three strings become a three-element array. Nothing here is ambiguous, which is why the interesting behaviour only shows up in the next two examples.

42
3.14
true
007

Type detection in action. The first three become a number, a number and a boolean. The last stays the string "007", because dropping that leading zero would turn a code into a different value entirely.

  spaced  

duplicate
duplicate

A realistically messy paste. Padding is trimmed, the blank line and the trailing newline are dropped, and turning on deduplication collapses the repeat and tells you one was removed.

Features

One line becomes one array element

Type detection for numbers

booleans and null

Leading-zero codes preserved as strings

Blank lines and trailing newline handled

Per-line whitespace trimming

Optional deduplication with a count of what was removed

Case-sensitive or case-insensitive matching

Optional wrapping as objects under a key you choose

Pretty-printed or compact output

Runs entirely in your browser

How to Use

1. Paste your list, one entry per line. 2. The JSON array appears immediately below. 3. Turn off type detection if the consumer expects every value as a string. 4. Enter a key name to wrap each line as an object instead of a bare value. 5. Copy the result, switching to compact output if it is going somewhere whitespace matters.

Common Mistakes

Letting a leading-zero code become a number. Postcodes, product codes and phone numbers lose their zero and become values that match nothing.
Forgetting the trailing newline. Without blank-line removal, a paste that ends in a newline adds an empty string to the end of the array.
Deduplicating case-sensitively when the data is email addresses. [email protected] and [email protected] are the same person, and the default will keep both.
Producing a plain array when the consumer wants objects. Most bulk-insert endpoints expect records with named fields, not bare values.
Pretty-printing JSON that is going into a URL or an environment variable. The whitespace is real characters and can push you over a length limit.

Frequently Asked Questions

Why is my number staying a string?

What happens to blank lines and stray spaces?

Can it remove duplicates?

Can I produce an array of objects instead of plain values?

How do I get one line per entry rather than pretty-printed?

Is there a limit on how many lines it can handle?