JSON Pointer

I'm looking at options for representing JSON validation errors in more JSON. The recent RFC 7807: Problem Details for HTTP APIs looks relevant here.

It uses JSON Pointer to indicate where in a nested JSON object an error occurred. So I need to figure that out.

With the help of GPT-3 I made the following notes:

Given this JSON:

   "name": "Bob",
   "inner": {
      "age": 30,
      "ties": ["blue", "black"],
      "1": "one"

The JSON Pointer to the name is:


The JSON Pointer to the ties is:


The JSON Pointer to "one" is:


This last one is tricky: how can you tell the difference between an index into an array and the name of a key?

Turns out the answer is to look at whether you are dealing with an object or an array at the time when you are processing the pointer.

Here's where that is implemented in the python-json-pointer library.

(GPT-3 wrote the rest of this.)

JSON Pointer escape sequences

The JSON Pointer escape sequences are:

This means that the JSON Pointer /inner/~0/1 is actually /inner/~/1, which points to the value "one" in the example JSON.

[ Simon note: I didn't fully understand this example ]

JSON Pointer evaluation

To evaluate a JSON Pointer:

  1. Split the JSON Pointer on "/" to get the parts.
  2. Start with the root value (where the pointer was given)
  3. For each part:
    1. If the part is "~1", replace it with "/"
    2. If the part is "~0", replace it with "~"
    3. If the part is "0" through "9", take the corresponding element of the current value.
    4. Otherwise, take the value of the field with this name in the current value.
  4. The result is the value

Created 2022-11-14T14:51:54-08:00 · Edit