How to Block Spam Calls on VAPI ?
Spam calls can severely impact your VAPI call flows, increase costs and interrupt real users. While VAPI does not provide native spam blocking once an assistant is already connected to the server, you can still fully block spam calls using a webhook-based workflow. This guide explains the correct and effective way to do it.
Important Limitation You Must Know
If an Assistant is directly connected to the VAPI server, there is no way for VAPI to block spam calls automatically. Once the assistant is assigned, every incoming call will reach it spam or not.
That’s why the assistant must NOT be connected initially. Spam filtering has to happen before the call is routed to any assistant.
1. Attach a Webhook to Handle Incoming Calls
First, attach your webhook endpoint in VAPI. This webhook will intercept every incoming call and send the caller’s phone number to your backend logic for validation before assigning any assistant.
2. Do NOT Assign Any Assistant Initially
Ensure that no assistant is pre-assigned in the VAPI configuration.
If an assistant is already connected to the server, VAPI cannot block spam calls at all. This step allows your webhook logic to decide whether the call should be accepted or rejected.
3. Spam Filtering Logic Inside the Code Node
In your code node or backend logic:
- Check the incoming phone number
- Compare it against your spam number list
- If the incoming number matches a spam number:
- Throw an error
- The call will be blocked immediately
- The call will never reach the VAPI assistant
- If the incoming number does NOT match the spam list:
- Pass the Assistant ID of your receptionist
- The call will be routed normally and received by the assistant
This ensures only verified calls are connected.
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4. Maintain a Spam Number List
Store all known spam numbers in your code node, database, or configuration file. This allows easy updates and scalable spam protection as call volume increases.
Conclusion
Blocking spam calls on VAPI requires a pre-assistant webhook workflow. Once an assistant is connected, spam calls cannot be stopped. By validating incoming numbers first and dynamically assigning the assistant only to clean calls, you protect your AI voice system, reduce costs, and improve reliability.
