JavaScript JSON Parse Tool
Paste JSON text or a JSON string copied from code, a database or a log line, quotes and backslashes included, and see the value that JSON.parse returns. The tool decodes escaped strings, unwraps JSON that was encoded twice, optionally parses JSON hidden inside string fields, warns about duplicate keys and oversized numbers, and points to the exact line and column when parsing fails.
- Runs in your browser
- No sign-up
- Free to use
How to use JavaScript JSON Parse Tool
- Paste JSON or an escaped JSON string such as "{\"id\":1}".
- Choose formatted JSON, a JavaScript object or a value overview.
- Read the notes about decoding, duplicates and precision.
- Copy or download the result.
JavaScript JSON Parse Tool features
Escaped input
Decodes quoted and backslash-escaped JSON strings first.
Double encoding
Unwraps JSON that was stringified more than once.
Nested JSON
Optionally parses string fields that contain JSON objects.
Precise errors
Line, column and a plain-English reason when JSON.parse would throw.
Data warnings
Duplicate keys and numbers beyond safe integer precision.
Three views
Formatted JSON, JavaScript object literal or a structure overview.
When to use JavaScript JSON Parse Tool
- Reading a JSON payload that a log printed as an escaped string.
- Fixing data that was accidentally JSON-encoded twice.
- Expanding webhook payloads whose fields contain JSON strings.
- Finding out why JSON.parse throws “Unexpected token”.
JavaScript JSON Parse Tool FAQ
What does JSON.parse do?
It turns JSON text into a JavaScript value: objects, arrays, strings, numbers, booleans and null. If the text is not valid JSON, it throws a SyntaxError.
What is double-encoded JSON?
JSON text that was passed through JSON.stringify again, so it became a string full of \" escapes. Parsing it once gives a string; parsing that string gives the data. The tool repeats the step automatically.
Why does my number change after parsing?
JavaScript numbers are 64-bit floating point. Integers above 9,007,199,254,740,991 cannot all be represented, so long IDs lose their last digits. Keep such IDs as strings.
What happens with duplicate keys?
JSON.parse keeps the last value without warning. The tool lists duplicates with their line numbers so you can fix the source.
Can it parse JSON with comments or single quotes?
No, because JSON.parse cannot. Use the JavaScript JSON Stringify Tool to turn such JavaScript literals into valid JSON first.
Is my data uploaded?
No. Parsing happens in your browser.
Making sense of JSON strings
JSON often reaches developers in a disguised form. Logging libraries print payloads as escaped strings, databases store JSON inside text columns that are themselves exported as JSON, and message queues wrap events in envelopes whose body is a JSON string. The data is all there, but surrounded by quotes and backslashes that make it unreadable and that JSON.parse handles one layer at a time.
This tool peels the layers off. If the input is wrapped in quotes, the JavaScript string escapes are decoded first. If parsing produces a string that looks like an object or array, it is parsed again, as many times as needed. With nested parsing switched on, string fields anywhere in the result that contain JSON objects or arrays are expanded too, which is how webhook and event payloads usually become readable.
When the text is not valid JSON, browsers produce terse messages such as “Unexpected token } in JSON at position 214”. The tool runs its own strict scanner to translate that into a reason and a line and column, for example a trailing comma before a closing brace or a missing quote, and highlights the line in the editor.
Some problems do not stop JSON.parse but still corrupt data. Duplicate keys are silently resolved in favour of the last occurrence, and integers longer than fifteen or sixteen digits are rounded because JavaScript stores numbers as double-precision floating point. Both are reported, because both are common causes of bugs that only appear with real data.
The result can be shown as formatted JSON for reading or saving, as a JavaScript object literal for pasting into code or tests, or as an overview that lists every key with its type, which is the quickest way to understand the structure of an unfamiliar payload.