Accepted syntax¶

Vexy JSON accepts everything that RFC 8259 JSON allows. This page lists the extensions it accepts on top of that, with the default parser options. Each example shows the input and the compact JSON that vexy-json -c prints for it. Objects are stored in a hash map, so the real output can list keys in a different order.

Comments¶

Line comments start with // or # and run to the end of the line. Block comments are enclosed in /* and */.

{
  // line comment
  a: 1, # another line comment
  /* block
     comment */
  b: 2
}

{"a":1,"b":2}

Option: allow_comments. CLI: --no-comments.

Trailing commas¶

A comma after the last element of an array or the last member of an object is ignored.

{"items": [1, 2, 3,], "done": true,}

{"items":[1,2,3],"done":true}

Option: allow_trailing_commas. CLI: --no-trailing-commas.

Unquoted keys¶

Object keys can be written without quotes. Letters, digits, _, $ and - work in unquoted keys.

{name: "Vexy", $id: 7, max-size: 10}

{"name":"Vexy","$id":7,"max-size":10}

Option: allow_unquoted_keys. CLI: --no-unquoted-keys.

Unquoted string values¶

A single bare word in value position becomes a string. Only true, false and null keep their JSON meaning.

{mode: fast, level: hello-world, missing: nil}

{"mode":"fast","level":"hello-world","missing":"nil"}

A value made of several words separated by spaces is rejected; quote it instead.

Single-quoted strings¶

Strings can be enclosed in single quotes. Inside them, \' is an escaped quote and double quotes need no escaping.

{'greeting': 'it\'s "fine"'}

{"greeting":"it's \"fine\""}

Option: allow_single_quotes. CLI: --no-single-quotes.

Implicit top-level object or array¶

The outer braces or brackets can be left out. Key-value pairs at the top level form an object; a comma-separated list of values forms an array.

host: 'localhost', port: 8080

{"host":"localhost","port":8080}

1, 2, 3

[1,2,3]

Option: implicit_top_level. CLI: --no-implicit-top-level.

Newlines as separators¶

A newline can take the place of a comma between array elements and between object members.

[
  "red"
  "green"
]

["red","green"]

Combined with implicit top-level objects, this reads a simple key: value file:

a: 1
b: 2

{"a":1,"b":2}

Option: newline_as_comma. CLI: --no-newline-as-comma.

Number formats¶

Besides standard JSON numbers, the lexer reads:

Input	Value	Notes
`0x1F`	`31`	hexadecimal
`0o17`	`15`	octal
`0b101`	`5`	binary
`1_000`	`1000`	underscores between digits
`.5`	`0.5`	no leading zero
`1.`	`1`	no digits after the point
`+3`	`3`	explicit plus sign
`-0x10`	`-16`	sign on a prefixed number

Integers that fit in a signed 64-bit integer become Number::Integer; other numbers become Number::Float. NaN and Infinity are not numbers in Vexy JSON: as bare words they become the strings "NaN" and "Infinity".

These formats have no on/off option.

Empty array slots¶

An empty slot between commas becomes null:

[1,,2]

[1,null,2]

Duplicate keys¶

When a key appears twice in one object, the last value wins:

{a: 1, a: 2}

{"a":2}

What is still rejected¶

More than one top-level value, such as {"a":1}{"b":2}. Use NDJSON mode (--ndjson or NdJsonParser) for one value per line.
Nesting deeper than max_depth (default 128) levels.
Input that ends inside an object, array or string. The CLI can close some truncated input with --repair; see Repairing incomplete input.
Mismatched brackets, such as [1, 2}.

The library parses empty input to null. The CLI prints No input provided for empty standard input and exits with status 0.