JSON schema sometimes wrapped in array

[Nikita Malyschkin]

Hi everyone

So I've encountered this anomaly where the JSON schema response is sometimes wrapped in an array.

I've looked in chrome://on-device-internals/ logs and see the reponse being wrapped.
I was able to get wrapped and unwrapped results with identical session setup and prompt.

Having a look in the logs and seeing how the sausage is made I expect that this non deterministic behaviour is coming from the model directly. Maybe the injected prompt for enforcing schemas can be tweaked to behave more predictably.

Here's an example from the logs(input/output redacted):
Executing model with input context of 218 tokens: <user>[==user input==] Remember to respond in JSON that follows this "JSON Schema" specification: {"title":"string","acknowledgement":"string","question":"string"}<end><model>
Model generates raw response with PromptApi: [{"title":"[==title==]","acknowledgement":"[==acknowledgement==]", "question":"[==question==]"}]

For now, this is my workaround:

Hope this saves someones time debugging their code :D

[Thomas Steiner]

Hi Nikita,

I saw a similar issue before and successfully addressed it by adding a concrete example output to my prompt (the API already repeats the JSON Schema [unless you explicitly omit this]). 

JSON Schema:

{
  "type": "object",
  "properties": {
    "hashtags": {
      "type": "array",
      "maxItems": 3,
      "items": {
        "type": "string",
        "pattern": "^#[^\\s#]+$"
      }
    }
  },
  "required": ["hashtags"],
  "additionalProperties": false
}

Example output:

{
  "hashtags": [
    "#pottery",
    "#dyi"
  ]
}

My prompt:

const result = await session.prompt(  
  `Suggest hashtags for this post:

${post}

Example response:

{

  "hashtags": [
    "#pottery",
    "#dyi"
  ]

}`,
  {  
    responseConstraint: schema,
  }
);

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Thomas Steiner, PhD—Developer Relations Engineer (blog.tomayac.com, toot.cafe/@tomayac)

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[Nikita Malyschkin]

Few-shot prompting is a great idea, thank you! :)
But this sounds like a problem for tomorrow 😄 😴