Drop a JSON file. Any size.
safe · secure · no server · works offline · fast
…or just start typing at the cursor.
safe · secure · no server · works offline · fast
…or just start typing at the cursor.
OmniViewer opens a JSON file right in your browser. Drop a
.json file and you get a formatted, syntax‑highlighted
view plus a small toolkit: a one‑click YAML
conversion, a CSV conversion for arrays of objects, a
stats report, and the raw and hex views. There is no
upload and no server — the data is read directly by your browser, and
the heavy work runs in a background Web Worker so the page never freezes.
The raw and hex views read only the bytes needed to paint the screen, so
even a multi‑gigabyte document opens instantly and privately.
true/false/null) and line‑numbered. A bar above it tells you whether the file is valid JSON and how big it is.
JSON — JavaScript Object Notation — was popularised by Douglas
Crockford in the early 2000s as a lightweight alternative to XML, drawn
from JavaScript’s object literal syntax but language‑independent.
It is standardised twice over: as ECMA‑404 and as
IETF RFC 8259, which agree on the grammar —
objects, arrays, strings, numbers, and the three literals
true, false and null. Its very
strictness (no comments, no trailing commas) is what makes it safe to
exchange between systems.
A tiny example of JSON:
{ "name": "OmniViewer", "local": true, "maxSizeGB": 20 }
| Aspect | JSON | YAML | CSV | XML |
|---|---|---|---|---|
| Shape | Nested objects & arrays | Nested, indentation-based | Flat rows & columns | Nested elements & attributes |
| Comments | No | Yes (#) | No | Yes |
| Human-friendliness | Good | Best | Best for tables | Verbose |
| Typical use | APIs & config | Config & CI | Spreadsheets & exports | Documents & legacy feeds |
| Standard | RFC 8259 / ECMA-404 | YAML 1.2 spec | RFC 4180 | W3C XML |
OmniViewer opens every file format; JSON is one of the formats with dedicated tooling. For deep work on huge JSON — collapsing, searching and streaming multi‑gigabyte documents — the same authors run the specialised fastjsonviewer.com, and hugecsv.com for CSV.
No. OmniViewer is a static page with no server-side processing: your .json file is read directly by your browser, and every tab — formatting, YAML, CSV and stats — runs locally in a Web Worker. The file never leaves your computer.
The raw and hex views are windowed — they read only the bytes needed to paint the screen — so they open files of effectively unlimited size, up to 20 GB and beyond; the engine behind them has been tested in-browser with a 40 GB file. The formatted view and the conversions (YAML, CSV) and stats process the document in memory, so on very large files they work on a bounded prefix and tell you when they do. The validity check above the view is skipped past a size threshold for the same reason.
Yes. The YAML tab renders the document as a block-style YAML file, quoting strings only where YAML requires it. The CSV tab flattens an array of objects into an RFC 4180 table whose columns are the union of every object’s keys, with nested values encoded into the cell. Both offer copy and download.
CSV is a table, so it only makes sense when the JSON is an array of objects (rows). If your document is a single object, a plain array of numbers, or anything else that isn’t a list of records, the CSV tab isn’t shown — the Formatted, YAML and Stats tabs still are.
Yes. A bar above the raw and formatted views reports whether the file parses as valid JSON (and its root type — object, array, and so on) or, if it doesn’t, the parse error. Past a size threshold the check is skipped to stay fast, and it says so.
JSON is defined by IETF RFC 8259 and, identically, by ECMA-404. Standard JSON does not allow comments or trailing commas — that strictness is deliberate, to keep it safe to exchange between systems. Variants like JSON5 and JSONC add comments, but they are not standard JSON.
Same engine, same authors. OmniViewer is the universal front door for any file, with a JSON toolkit for everyday files. fastjsonviewer.com is the specialised tool for very large JSON — collapsing, searching, querying and streaming multi-gigabyte documents.