CSV to JSON converter: turn a lead list into an array or one object per line
In short: Upload or paste a list with a header row and get a JSON array of objects, or one object per line, with blank cells and plain numbers written the way you choose. Limit: It reads the first sheet of a workbook only.
Upload a CSV or .xlsx file, or paste the cells with the header row first. Each row becomes one object whose keys are the column names. Pick one JSON array or one object per line (NDJSON), and choose whether plain numbers and true or false stay text, and whether blank cells are null. Download or copy the result.
Price: this tool is free. Checking a whole email list is from $9/mo, and the first 100 checks are free with Google, no card. Check your list free nowSee pricing
Sample result
Three example rows become 3 JSON objects, with 45 as a number, a blank cell as null and 0012 kept as text.
- Objects
- 3
- Keys per object
- 5
- Leading zero
- Kept as text
What this means for you
A new format is not a working mailbox; a check shows which addresses exist.
- Array or one per line
- Numbers and booleans optional
- Blank as null or empty
- Leading zeros kept
- JSON
- CSV
- Lead list
By SimpleVerifier Team · Last updated · Runs in your browser; nothing you paste is sent to us
Sending this list to an API or a database?
- Download the JSON here, or use the check button under the result, which carries its addresses across.
- Upload or paste it at /verify. Every address gets a live mailbox check, and the first 100 email checks are free with a Google sign-in, no card.
How do I convert a CSV to JSON?
- Upload the file as a CSV or .xlsx, or paste the cells with the header row first.
- Choose one JSON array or one object per line.
- Choose whether plain numbers and true or false are written as numbers and booleans, and whether blank cells are null.
- Check the first rows shown, then download the file or copy the JSON.
Example
- You enter
- Three rows with Email, Name, Company, Employees and Opted in columns, one blank Employees cell and one Employees value of 0012, with typed values and blank as null on.
- You get
- A JSON array of 3 objects. Employees is the number 45, then null, then the text "0012" (a leading zero keeps it as text). Opted in is written as true, false and true.
- Limits
- Runs in your browser with no row cap; an uploaded file can be up to 25 MB. Nothing is uploaded.
How are the keys and values chosen?
The header row gives the keys. A blank header becomes column_1, column_2 and so on by position, and a header that appears twice gets _2 on the second one, so no key is lost.
By default every value is text exactly as it was in the cell. That is the safe choice for lead lists: a phone number such as 0123456789 or a long ID would lose its leading zero or its last digits as a number.
What does the typed option change?
With it on, a plain whole number or decimal becomes a JSON number, and true or false (any case) becomes a boolean. Numbers with a leading zero, and numbers of 16 or more digits, always stay text.
Blank cells become an empty string, or null if you tick that option. Most APIs treat a missing value and an empty string differently, so check what yours expects.
Array or one object per line?
A JSON array is one document, which suits a request body or a config file. One object per line (NDJSON or JSON Lines) suits a large list because a tool can read it a line at a time.
Whichever you choose, the conversion happens in your browser and the file is never uploaded. For the reverse, see the JSON to CSV converter.
Who uses this tool, and for what?
- Developers
- Turn a lead export into a test fixture or a request body without writing a script.
- Cold emailers
- Prepare a list for a webhook, a no-code tool or a custom sender that wants JSON.
- Data teams
- Make an NDJSON file from a CSV before loading it into a warehouse.
What can’t this tool tell you?
- It reads the first sheet of a workbook only.
- Dates are kept as the text in the cell; they are not converted to a date format.
- Every row becomes a flat object; nested JSON is not produced.
- It does not check whether an address exists.
Common questions
- Are numbers written as numbers?
- Only if you tick the option. By default every value stays text, so phone numbers and IDs keep their leading zeros.
- What happens to a repeated column name?
- The second one gets _2, the third _3, so every column appears in each object.
- Does it handle commas and quotes inside cells?
- Yes. The file is read as standard CSV, where a cell in quotes may hold commas, quotes and line breaks. See RFC 4180.
- Can I upload an Excel file?
- Yes. A .xlsx file is read from its first sheet, or you can paste the cells.
- Is my list uploaded?
- No. The conversion runs in your browser and nothing is sent anywhere unless you choose to check the addresses afterwards.
- Does it check the addresses?
- No. It only changes the format. A mailbox check shows which addresses exist.
Sources
A tidy list can still be full of dead addresses.
Extracting, deduplicating and syntax checks all work on the text of an address. None of them can tell whether the mailbox exists. Only the server that hosts it can answer that, through an SMTP check, and that is what the paid product does.
- Upload the cleaned file as it is: CSVs up to 100,000 rows
- A real SMTP mailbox check on every row, with catch-all detection
- Small list? Starter at $9/mo covers 2,500 emails a month, cancel anytime
Plans from $9 a month, cancel anytime, no contract. Sign in with Google and your first 100 email checks are free, no card. The free tools stay free either way.