Dynamic Params

Your app often knows things Bag of words doesn’t, like the id of the chat a question came from, the message id, or the ticket being discussed. Dynamic params let your app send those values with each question. Bag of words then adds them to every MCP tool call made while answering it.

Available on MCP connections, as part of User context forwarding.

How it works

An admin lists which keys the connection accepts, with a default for each.
Your app sends values for those keys in prompt.metadata when it calls the completions API.
Every MCP tool call for that question carries the values in the metadata argument (custom_metadata by default).

For each listed key:

Situation	Result
Your app sent a value	The sent value is used
Not sent, default is set	The default is used
Not sent, default is `null`	The key is left out
Key isn’t in the list	Dropped, never sent
A forwarded field has the same name	The field’s value wins

The model never sees these keys and cannot change their values.

Set it up

Open the MCP connection and expand Advanced → User context forwarding.
Under Tool metadata, turn on Dynamic params.
Enter the allowed keys as a JSON object of { "key": default }:

{
  "chat_id": null,
  "message_id": null,
  "env": "prod"
}

Save.

Send values from your app

Add metadata to the prompt of a completions request. It works the same for streaming and non-streaming requests.

curl -X POST "$BOW_URL/api/reports/$REPORT_ID/completions" \
  -H "Authorization: Bearer $BOW_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "prompt": {
      "content": "What is the status of order 555?",
      "metadata": { "chat_id": "c-77", "message_id": "m-912" }
    }
  }'

curl -N -X POST "$BOW_URL/api/reports/$REPORT_ID/completions" \
  -H "Authorization: Bearer $BOW_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Accept: text/event-stream" \
  -d '{
    "stream": true,
    "prompt": {
      "content": "What is the status of order 555?",
      "metadata": { "chat_id": "c-77", "message_id": "m-912" }
    }
  }'

import os, requests

resp = requests.post(
    f"{os.environ['BOW_URL']}/api/reports/{os.environ['REPORT_ID']}/completions",
    headers={"Authorization": f"Bearer {os.environ['BOW_API_KEY']}"},
    json={
        "prompt": {
            "content": "What is the status of order 555?",
            "metadata": {"chat_id": "c-77", "message_id": "m-912"},
        }
    },
)
resp.raise_for_status()

What the MCP server receives

With the allow-list above and a locked user_email field, each tool call includes:

"custom_metadata": {
  "chat_id": "c-77",
  "message_id": "m-912",
  "env": "prod",
  "user_email": "[email protected]"
}

Limits

metadata must be a JSON object with non-empty keys, up to 8 KB. Anything else returns 422.
The allow-list must be a JSON object, up to 8 KB. An invalid list is rejected when you save.
Values are stored with the question. Members of the report can see them through the API; public share links never show them.

Values come from your app and aren’t verified. Don’t use them to decide who the user is. For identity, use a locked forwarded field, which always wins over a dynamic param of the same name.

Get Started

Work With Agents

Agents

Guides

Connect Any Data

Models

Observe and Govern

Channels

Open Source and Enterprise

How it works

Set it up

Send values from your app

What the MCP server receives

Limits

​How it works

​Set it up

​Send values from your app

​What the MCP server receives

​Limits

How it works

Set it up

Send values from your app

What the MCP server receives

Limits