Special Tool Call Support That Gets Triggered Imme...
# supportk
ketchuptea
04/01/2025, 1:02 PMWe're using VAPI for our appointment booking chatbot and need a tool call to trigger immediately at the start of a call to provide better context to the chatbot. Currently, it only runs after or at the first human reply, even when we explicitly prompt it to run earlier (tried async, sync, etc.).
This would be very useful for many use cases where prerequisite data needs to be fetched from webhooks at the start of a call. Let us know if there's a way to achieve this or if it can be considered as an enhancement.
v
Vapi Support Bot
04/01/2025, 1:04 PMHi there! 👋
I understand you're trying to trigger a tool call immediately at the start of a call in VAPI for your appointment booking chatbot. While I couldn't find a guaranteed solution for triggering tool calls right at call start, I can share what I found about current limitations and possible approaches.
## Current Limitations
Based on the information I found, this appears to be a known issue. Several users have reported similar challenges with tool calls not triggering immediately at the start of a call, even when prompted to run earlier. According to [user discussions](https://discord.com/channels/1211482211119796234/1211483291191083018/threads/1329542939160084624), tool calling functionality can break frequently after new feature rollouts, and tools can sometimes automatically become async.
## Possible Approaches
Here are some approaches that might help:
### 1. Custom Tools with Explicit Tool Calls
You could try creating a custom tool and associating it with your assistant, using explicit tool calls with prompts to trigger the tool. According to [this discussion](https://discord.com/channels/1211482211119796234/1211483291191083018/threads/1333245023319494707), Vapi will send a server request where you can use the SDK to trigger actions by inferring the server message tool call payload.
### 2. Synchronous Tool Configuration
Ensure your tool is set to
synchronousasynctool_call_resultVapi Support Bot
04/01/2025, 1:04 PMOne alternative approach is to set up your own webhook endpoint first, process the call as needed, and then forward it to VAPI. This allows you to intercept the call and fetch data before VAPI processes it, as suggested in [this conversation](https://discord.com/channels/1211482211119796234/1211483291191083018/threads/1343397177182912553).
### 4. Using assistantOverrides
You can include relevant data in the
variableValuesassistantOverrides Copy code
javascript
vapiInstance = vapiSDK.run({
apiKey: apiKey,
assistant: assistant,
config: buttonConfig,
assistantOverrides: {
variableValues: {
userId: "yourUserIdHere"
}
}
});k
Kyle Brunker
04/01/2025, 9:00 PMYou can raise an feature request for it over here: https://roadmap.vapi.ai