structa is a hidden gem. It’s one of many great utilities created by Dave Jones. It’s a command line tool for analysing JSON files. Sometimes you need to inspect the structure of a large nested JSON file, and it’s too unwieldy to work out what kind of data it contains. structa is perfect for showing you.

The People in Space API shows the number of people currently in space, and their names and craft name:

structa astros.json


├─ 'number': 5
├─ 'message': success
└─ 'people': [
   ├─ 'craft': ISS
   └─ 'name': {Doug Hurley|Bob Behnken|Chris Cassidy|Anatoly...}

As you can see, most of this data is static – so the values are just given as is. But the people value is an array, so it shows the keys and the data types. Again, since craft is the same every time, it’s just given, but name varies, so the value is given as a set of the variations.

The Python Package Index (PyPI) provides a JSON API for packages:

wget -O numpy.json
structa numpy.json


├─ 'last_serial': 7391399
├─ 'urls': [
   ├─ 'requires_python': >=3.5
   ├─ 'filename': <str>
   ├─ 'yanked_reason': None
   ├─ 'comment_text':
   ├─ 'python_version': {cp36|source|cp35|cp38|cp37}
   ├─ 'md5_digest': <str 'hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh'>
   ├─ 'size': <int 5.2M..19.6M>
   ├─ 'downloads': -1
   ├─ 'url': <URL>
   ├─ 'has_sig': False
   ├─ 'upload_time': <datetime '%Y-%m-%dT%H:%M:%S' 2020-06-04 00:10:51..2020-06-04 00:27:58>
   ├─ 'upload_time_iso_8601': <str '2020-06-04T00:dd:dd.ddddddZ'>
   ├─ 'digests':
   │  ├─ 'md5': <str 'hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh'>
   │  └─ 'sha256': <str ...>
   ├─ 'packagetype': {sdist|bdist_wheel}
   └─ 'yanked': False
├─ 'info':
│  └─ <str>: <value>
└─ 'releases':
   └─ <str>: [
      ├─ 'requires_python': {>=3.5|>=2.7,!=3.0.*,!=3.1.*,!=3.2.*,!=3.3.*|>=3.6|None}
      ├─ 'filename': <str>
      ├─ 'yanked_reason': None
      ├─ 'comment_text': {|Simple installer, no SSE instructions. |Simple windows...}
      ├─ 'python_version': <str>
      ├─ 'md5_digest': <str 'hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh'>
      ├─ 'size': <int 1.8M..23.4M>
      ├─ 'downloads': -1
      ├─ 'url': <URL>
      ├─ 'has_sig': {False|True}
      ├─ 'upload_time': <datetime '%Y-%m-%dT%H:%M:%S' 2006-12-02 02:07:43..2020-06-04 00:35:35>
      ├─ 'upload_time_iso_8601': <str>
      ├─ 'digests':
      │  ├─ 'md5': <str 'hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh'>
      │  └─ 'sha256': <str ...>
      ├─ 'packagetype': {bdist_wheel|bdist_wininst|sdist}
      └─ 'yanked': False

Here you can see a wide variety of helpful information inferred from the data, including:

  • Under urls:
    • filename is a string (too many options to show as a set)
    • python_version is always one of: {cp36|source|cp35|cp38|cp37}
    • size is an integer between 5.2 million and 19.6 million (bytes)
    • md5_digest is a 32-character hex string
    • url is detected as being a URL
    • upload_time is a datetime string in the format '%Y-%m-%dT%H:%M:%S' ranging between 2020-06-04 00:10:51 and 2020-06-04 00:27:58
    • packagetype is either sdist or bdist_wheel
  • Under info:
    • There’s a variable key name, which contains a variety of values
  • Under releases:
    • There’s a variable key name, which contains an array…

Unfortunately, structa is not published on PyPI yet, so for now you have to install it from GitHub:

git clone
cd structa
pip install .