CSV to JSON
CSV to JSON Converter
Paste or upload CSV and get clean JSON instantly — quotes, commas, and line breaks handled correctly. Nothing is uploaded.
- Runs in your browser
- Nothing uploaded
- No sign-up
- Free, no daily limits
- 1Add your file
- 2Choose settings
- 3Download
100% Private: Your CSV is parsed entirely in your browser — nothing is uploaded to any server.
Convert CSV to JSON Online Free
CSV to JSON is a free, in-browser converter that transforms spreadsheet records into structured JSON arrays of objects without uploading files to a server. Paste CSV or drop files up to 25 MB. The pure JavaScript state machine parses complex quotes, embedded commas, and multiline cells per RFC 4180 rules. Select between raw string output or coerced numeric types, inspect live results, and download clean JSON ready for software development.
Real Conversion Sample: Quoted Multiline Cells and Type Coercion
Here is how raw CSV records translate into structured JSON. Notice how embedded commas inside quotes stay in one string, newlines remain preserved, and numbers coerce cleanly without losing phone numbers:
id,full_name,address,formula_test,amount 101,"Doe, Jane","Apt 4B\n123 Market St",=2+5,1500.50 102,"Smith, John","PO Box 99",@SUM(A1:A5),-42.00 103,"O'Connor, Tim","742 Evergreen",+15550100,0
[
{
"id": 101,
"full_name": "Doe, Jane",
"address": "Apt 4B\n123 Market St",
"formula_test": "=2+5",
"amount": 1500.5
},
{
"id": 102,
"full_name": "Smith, John",
"address": "PO Box 99",
"formula_test": "@SUM(A1:A5)",
"amount": -42
},
{
"id": 103,
"full_name": "O'Connor, Tim",
"address": "742 Evergreen",
"formula_test": "+15550100",
"amount": 0
}
]Edge Cases We Handle (And How)
| Input Quirk | What Our Parser Does | Code Location & Rule |
|---|---|---|
| Embedded commas and quotes | RFC 4180 state machine treats delimiters inside quotation marks as literal data. Escaped quotes ("") become single quotes. | lib/csv.ts:201-207 |
| Ragged rows with extra cells | Surplus cells beyond header width are saved under generated column_N keys rather than discarded, logging an extra-cells warning. | lib/csv.ts:386-405 |
| Duplicate header columns | Registers taken keys and appends _2, _3 suffixes so data in duplicate columns is not overwritten in the JSON object. | lib/csv.ts:317-338 (dedupeHeaders) |
| Header key named __proto__ | Defines property via Object.defineProperty to bypass inherited prototype setters, blocking prototype pollution. | lib/csv.ts:308-314 (setColumn) |
| Leading UTF-8 BOM (\uFEFF) | Stripped from text start so the first key is not prepended with an invisible zero-width character. | lib/csv.ts:21 (stripBom) |
| Unterminated quoted fields | Tolerant default collects remaining text into one cell and warns instead of crashing live textarea typing. | lib/csv.ts:221-226 |
How to Convert CSV to JSON Step-by-Step
Paste or Upload CSV
Drop a .csv file or paste raw delimited text into the input panel.
Select Delimiter
Keep 'Auto' detection or choose comma, semicolon, tab, or pipe.
Set Output Mode
Toggle 'First row is header' for objects, or turn off for an array of arrays.
Copy or Download
Copy the JSON string or download data.json directly to disk.
User-Facing Parsing Diagnostics
When processing malformed CSV exports from legacy systems, our parser detects structural anomalies and surfaces specific diagnostic messages rather than failing silently:
"Unterminated quoted field starting on row N: everything after the opening quote was read as a single cell."
Triggers when an opening quote has no matching closing quote before file completion.
"N rows had more cells than the header row; the surplus values were kept under generated column_N keys."
Preserves ragged records in place so unexpected fields are never lost during export.
Key Features for Developers and Analysts
Zero Data Transmission
Your records remain in local tab memory. Ideal for confidential customer data.
Strict RFC 4180 Support
Handles escaped quotes, commas, and multiline records without schema collapse.
Automatic Delimiter Sniffing
Evaluates candidate delimiter frequencies outside quotation marks across sampled rows.
Lossless Type Coercion
Decimal numbers become real numeric types; zero-padded strings keep their text format.
Objects or Matrix Output
Produce an array of keyed objects, or switch to an array of raw value arrays.
Debounced Keystroke Sync
Parsing runs on a 120 ms debounce timer so large text edits do not freeze your UI.
When Not to Use This Web Tool
Browser JavaScript has strict memory allocations. If your CSV file exceeds 25 MB (26,214,400 bytes), your tab may encounter memory pressure. For multi-gigabyte files or automated ETL jobs, use command-line streaming tools like csvjson file.csv > file.json from the csvkit suite or stream records through a Python generator script.
Frequently Asked Questions
How do I convert CSV to JSON in my browser?
Paste your CSV text or upload a .csv file up to 25 MB into the editor. The tool parses records in local memory and outputs structured JSON. By default, each row becomes an object keyed by the first header row. You can copy the formatted JSON with one click or download it as a .json file.
How does the parser handle quotes, commas, and line breaks inside fields?
Our parser complies with RFC 4180 standards. Fields enclosed in double quotes can safely contain the delimiter, Windows (\r\n) or Unix (\n) line breaks, and escaped quotation marks (""). The parser keeps the multiline text inside its corresponding field instead of breaking your record structure.
What happens if my CSV has duplicate or blank header names?
To prevent duplicate keys from overwriting each other in JSON objects, our parser deduplicates headers. Repeated column names receive numeric suffixes such as name_2 and name_3. Any empty header cell automatically becomes column_N based on its 1-based index position.
Can I convert numbers and booleans into real JSON types?
Yes. By default, values stay as raw text strings to avoid identifier corruption. Enabling 'Convert numbers & booleans' coerces valid decimal numbers up to 15 digits into JavaScript numbers, true/false strings into boolean primitives, and empty cells into null. Values with leading zeros like 007 remain strings.
What does the parser do when rows have extra or missing columns?
Missing cells in a row are padded with empty strings (or null when typed). If a row contains extra cells beyond the header count, our parser retains the surplus values under generated column_N keys rather than dropping data, logging an extra-cells warning.
What is the maximum file size for browser conversion?
The tool handles CSV files up to 25 MB (26,214,400 bytes) directly in your browser tab. For gigabyte log files or large database dumps, command-line streaming utilities like csvkit (csvjson) or DuckDB provide faster execution without tab memory limits.