ExpressionJSON (.json)

Import and Export support ExpressionJSON.
ExpressionJSON provides lossless round-tripping of Wolfram Language expressions to and from JSON.
By default, Import and Export use the "JSON" format for files ending in .json, rather than the "ExpressionJSON" format.

Background & Context

Import ["file","ExpressionJSON"] imports a file that uses the ExpressionJSON format, producing an ordinary Wolfram Language expression.
Export ["file",expr,"ExpressionJSON"] exports an arbitrary expression to ExpressionJSON.
Elements of expressions are represented as follows in ExpressionJSON:
"string" "'string'" (UTF-8, with JSON escaping)

True ,False true, false

Null null

symbol "symbol" (UTF-8)

f[e₁,e₂,…,opt₁val₁,…] ["f",e₁,e₂,…,["Rule",opt₁,val₁],…]
Machine integers are represented literally. Larger integers are represented as "digits".
See the following reference pages for full general information:
Import , Export import from or export to a file

CloudImport , CloudExport import from or export to a cloud object

ImportString , ExportString import from or export to a string

ImportByteArray , ExportByteArray import from or export to a byte array

General Import elements:
"Elements" list of elements and options available in this file

"Summary" summary of the file

"Rules" list of rules for all available elements

Export options:
"Compact" False whether to omit line breaks and tabs

"NullSymbols" {} a list of symbols to represent as JSON null

"PrecisionHandling" True whether to allow bignums or issue a message
"Compact"->n includes line breaks and tabs up to indent level n.

Import a JSON list:

Import a String :

Import a Quantity :

Export an expression to a JSON string:

Export a list while converting None to JSON null:

Export a list of numbers of arbitrary precision:

Export a list of numbers and issue an error if any of them is not a machine-precision number:

Control the output format with "Compact" to limit indentation:

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