How to inject custom tools per call/session in Vap...
# supportn
Neumark
10/12/2025, 3:20 PMHey folks! I’m integrating Vapi into an AI agent builder platform. Users create agents with a unique set of “tools” (each tool = an HTTP API endpoint I host). In text chat I already do dynamic tool routing. Now I want the same agent to work in Vapi voice + phone calls, but:
Each call/session must get a custom tool set (based on the specific agent + tenant).
I can’t pre-save all tools in Vapi because every user/agent differs.
I’d like to inject tools at call start, and have tool calls be webhooked to my backend (I handle auth/tenancy/rate-limits).
Questions:
What’s the recommended way to send per-call tool definitions (schema + name + description) to Vapi? Is there a supported “assistant overrides” / “runtime tools” mechanism at call initialization?
Can I resolve tools server-side on call.started (or equivalent) and return a tool list for that session?
c
Chiranjeet Mishra
10/12/2025, 3:20 PMHi there,
Thank you for your message. Our team is currently out of the office. We operate Monday through Friday, from 9:00 AM to 8:00 PM Pacific Standard Time (PST).
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Vapi
Customer Support Team
Chiranjeet Mishra
10/14/2025, 6:53 PMHi Neumark,
To extend your Vapi voice assistant's capabilities, you can utilize various tools offered by Vapi, such as Default Tools, Custom Tools, and Integration Tools. Here’s a quick overview of what each type offers:
1. **Default Tools**: Pre-built functions like
transferCallendCallsmsapiRequest2 Views