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json(n) 1.3.4 tcllib "JSON"


json - JSON parser

Table Of Contents


  • package require Tcl 8.4
  • package require json ?1.3.4?


The json package provides a simple Tcl-only library for parsing the JSON http://www.json.org/ data exchange format as specified in RFC 4627 http://www.ietf.org/rfc/rfc4627.txt. There is some ambiguity in parsing JSON because JSON has type information that is not maintained by the Tcl conversion. The json package returns data as a Tcl dict. Either the dict package or Tcl 8.5 is required for use.


::json::json2dict txt

Parse JSON formatted text txt into a Tcl dict and return the value.

If txt contains more than one JSON entity only the first one is returned.

::json::many-json2dict txt ?max?

Parse JSON formatted text txt containing multiple JSON entities into a list of dictionaries and return that list.

If max is specified exactly that many entities are extracted from txt. By default the command will attempt to extract all, without limits. A value of "max == 0" does not make sense and will cause the command to throw an error.


An example of a JSON array converted to Tcl. A JSON array is returned as a single item with multiple elements.

       "precision": "zip",
       "Latitude":  37.7668,
       "Longitude": -122.3959,
       "Address":   "",
       "City":      "SAN FRANCISCO",
       "State":     "CA",
       "Zip":       "94107",
       "Country":   "US"
       "precision": "zip",
       "Latitude":  37.371991,
       "Longitude": -122.026020,
       "Address":   "",
       "City":      "SUNNYVALE",
       "State":     "CA",
       "Zip":       "94085",
       "Country":   "US"
{Country US Latitude 37.7668 precision zip State CA City {SAN FRANCISCO} Address {} Zip 94107 Longitude -122.3959} {Country US Latitude 37.371991 precision zip State CA City SUNNYVALE Address {} Zip 94085 Longitude -122.026020}

An example of a JSON object converted to Tcl. A JSON object is returned as a multi-element list (a dict).

    "Image": {
        "Width":  800,
        "Height": 600,
        "Title":  "View from 15th Floor",
        "Thumbnail": {
            "Url":    "http://www.example.com/image/481989943",
            "Height": 125,
            "Width":  "100"
        "IDs": [116, 943, 234, 38793]
Image {IDs {116 943 234 38793} Thumbnail {Width 100 Height 125 Url http://www.example.com/image/481989943} Width 800 Height 600 Title {View from 15th Floor}}


To write json, instead of parsing it, see package json::write.

Bugs, Ideas, Feedback

This document, and the package it describes, will undoubtedly contain bugs and other problems. Please report such in the category json of the Tcllib Trackers. Please also report any ideas for enhancements you may have for either package and/or documentation.

When proposing code changes, please provide unified diffs, i.e the output of diff -u.

Note further that attachments are strongly preferred over inlined patches. Attachments can be made by going to the Edit form of the ticket immediately after its creation, and then using the left-most button in the secondary navigation bar.


data exchange, exchange format, javascript, json


CGI programming