What is the JSON file format?
Files with the .json extension contain data stored in plain-text format, using notation derived from a subset of JavaScript, with UTF-8 encoding. The current authoritative description of the format is ECMA-404 and IETF RFC 8259 (2017), which superseded the earlier RFC 4627. Among other uses, .json is widely used to transfer information across networks and to store configuration, settings, and serialized application state.
A .json document can hold:
- Strings,
- Numbers (IEEE 754 double-precision floating-point),
- Boolean values (
trueandfalse), null,- Arrays of the above elements,
- Objects (key-value maps).
Objects and arrays can be nested on multiple levels. Although the syntax of .json files is based on JavaScript, they are used within applications written in virtually every programming language. In JavaScript, parsing and serialization are handled by the built-in JSON.parse() and JSON.stringify() methods, available since ECMAScript 5 - no external library is required. The format has no support for comments. Related text-based data formats include YAML, XML, and CSV.
Security & safety
RISK: LOWA JSON file is pure data - it cannot contain or execute code, so opening one in an editor is safe. The risks are informational: data exports often contain private data, API keys or session tokens (do not paste such files into online viewers or share them); and for developers, parsing untrusted JSON with eval() instead of JSON.parse(), or oversized files used for denial-of-service, are classic pitfalls. Watch for double extensions (.json.exe) in downloads.
Format details
in a nutshellFULL NAMEJavaScript Object Notation file
DEVELOPERSpecified by Douglas Crockford (2001); standards: ECMA-404, IETF RFC 8259since 2001 (json.org); first IETF spec RFC 4627 (2006); current RFC 8259 / ECMA-404 (2017)
CATEGORYData Files
MIME TYPEapplication/json
TYPEstructured plain-text data format (UTF-8)
STANDARDOpen · royalty-free
Programs that open JSON files
Windows4 apps
Mozilla Firefox
Open-source Drag the .json file into a Firefox tab - the built-in JSON viewer (since Firefox 53, 2017) shows a collapsible tree with search. 
Notepad
Open-source Lightweight editor with JSON syntax coloring; install the built-in 'JSON Viewer' plugin (Plugins Admin) to format and tree-view. 
Visual Studio Code
Free Open the file; press Shift+Alt+F to format (pretty-print) minified JSON, and use folding arrows to collapse sections. Best free choice for editing. 
Altova XMLSpy
Paid Commercial XML/JSON IDE with grid view and schema validation - relevant for enterprise developers, overkill for viewing. 
macOS3 apps
TextEdit
Built-in Right-click - Open With - TextEdit. Caution when editing: disable smart quotes (Edit - Substitutions), which silently corrupt JSON. 
BBEdit
Freemium Successor to TextWrangler (discontinued 2017); free mode covers JSON viewing/editing with syntax colors.
Visual Studio Code
Free Open and pretty-print with Shift+Option+F; handles huge files better than TextEdit. 
Linux4 apps
jq
Open-source Command-line JSON processor: 'jq . file.json' pretty-prints; filters extract fields ('jq .items[].name'). 
Android1 app
Files / any text editor app
Free Tap the file and choose a text/HTML viewer; for editing use an editor app such as Acode. JSON needs no special app.
Web2 apps
JSON Editor Online
Freemium Paste or open the file in the browser - tree view, formatting, validation and JSON-to-CSV export. Avoid pasting confidential data into any online tool.
JSON Crack
Freemium Visualizes JSON as an interactive node graph - useful for understanding deeply nested exports. Technical details
deep spec| MIME type | application/json |
| Character encoding | UTF-8; RFC 8259 mandates UTF-8 without BOM for network interchange |
| File signature (magic bytes) | None - plain text; a valid document starts with '{' (object) or '[' (array), optionally preceded by whitespace |
| Supported data types | string, number, boolean (true/false), null, array, object |
| Number representation | IEEE 754 double-precision (64-bit) floating-point; the spec defines no distinct integer type |
| String encoding | Unicode; non-ASCII characters may appear as literal UTF-8 or as \uXXXX four-hex-digit escape sequences |
| Comment support | None - comments are explicitly excluded from the JSON specification |
| Whitespace | Insignificant whitespace (space, tab, CR, LF) is permitted between any two tokens |
| BOM handling | RFC 8259 explicitly prohibits a UTF-8 BOM at the start of a JSON interchange document |
| Object key uniqueness | Keys within an object should be unique; RFC 8259 does not forbid duplicates but leaves the behavior implementation-defined |
| Nesting | Unlimited recursive nesting of objects and arrays; practical depth is limited by the parser's stack size |
| Built-in JavaScript API | JSON.parse() and JSON.stringify() are native since ECMAScript 5 (2009); no third-party library needed |
| Interoperability | Language-agnostic; parsers and serializers exist for virtually every major programming language |
| Common uses | REST API payloads, application configuration files, data serialization, streaming log lines (JSONL / NDJSON), web app manifests |
| Released | 2001 (json.org); first IETF spec RFC 4627 (2006); current RFC 8259 / ECMA-404 (2017) |
| Open standard | Yes · royalty-free |
| Specification | www.rfc-editor.org |
JSON conversions
Possible
.JSON .CSVGUIDE
Yes -- the fastest route for simple flat JSON is JSON Editor Online (free, browser) or Excel Power Query…
How to convert
.JSON .XMLGUIDE
Yes, JSON converts to XML -- the fastest way for most users is a free online converter such as…
How to convert
.JSON .YAMLGUIDE
Yes, JSON converts to YAML without data loss -- the fastest method on any platform is one yq command: yq -oy…
How to convert
.JSON .SQLITE3GUIDE
Yes - the fastest way is the command-line tool sqlite-utils, which imports a JSON array directly into a…
How to convert
.JSON .XLSXGUIDE
Yes, Excel can import JSON directly using the built-in Power Query tool (Data > Get Data > From File > From…
How to convert
Not possible
Community Q&A
asked by usersNo questions yet - be the first to ask about JSON files.
Frequently asked questions
What program opens a JSON file?
Any text editor - Notepad (Windows) or TextEdit (Mac) work immediately. For comfortable reading use VS Code or Notepad++ (formatting, collapsible tree), or drag the file into Firefox for its built-in JSON viewer.
How do I convert JSON to Excel?
In Excel: Data - Get Data - From File - From JSON, then convert and expand the records (Power Query). For simple flat JSON, an online JSON-to-CSV converter also works - but avoid uploading sensitive data.
Why is my JSON file one long unreadable line?
It is minified - whitespace was stripped to save bandwidth. Pretty-print it: Shift+Alt+F in VS Code, the 'Format' button in JSON Editor Online, or 'jq . file.json' in a terminal.
Is it safe to open a JSON file?
Yes - JSON is plain text data and cannot run code. Just be careful what you do with the contents (exports may hold passwords/tokens) and make sure the file is not a disguised executable like data.json.exe.
Can I edit a JSON file in Notepad?
Yes, but JSON syntax is strict: double quotes only, no trailing commas, no comments. One wrong comma breaks the app reading it - validate after editing (VS Code underlines errors live).
What is the difference between JSON and XML?
Both carry structured data as text. JSON is lighter, maps directly to data structures and dominates web APIs; XML supports attributes, namespaces and schemas and persists in documents and enterprise systems.
What is a JSONL / NDJSON file?
JSON Lines - one complete JSON object per line, used for logs and big datasets because it can be streamed line by line. A plain JSON parser will reject it; process it per line or with jq.
References
1IETF RFC 8259 - The JSON Data Interchange Format (STD 90)www.rfc-editor.org
2ECMA-404 - The JSON data interchange syntaxecma-international.org
