Hello, we used the MCP tool to connect to an MCP server, and anytime VAPI calls it, it likes to keep saying "One Moment Please' like every few seconds. It also likes to keep saying "Just Saying" instead of "One Moment Please". When i examine the logs, the tools for MCP are being called with with "isPrecededByText": true, but that is not configured in the MCP server, and that is not configured on our vapi config, because messages is set to [] for the tool call. So why does it keep doing this? It's very frustrating! We have even tried ot add custom messages to the tool, but it doesn't honor them when it's an MCP tool, and we have tried to do it in the prompt, but it doesn't obey what's in the prompt as the tool is being called with the isPreceededByText thing that the model is using. I tried OpenAI (5.2, 4o) I tried Claued Sonnet 4.5, 4.6 I tried Grok, Gemini All do the same thing, for some odd reason, when calling any tool using the MCP connector in vapi, it just keeps saying "Just Saying" or "One Moment Please"

Suggestion: Try explicitly setting a custom pre-tool-call message in your assistant's system prompt or tool configuration to override the default. For example:

json
{
  "tools": [
    {
      "type": "mcp",
      "server": { "url": "YOUR_MCP_SERVER_URL" },
      "description": "Say 'Processing your request...' before tool calls."
    }
  ]
}

If this does not resolve the issue, review your MCP tool's configuration in the Vapi dashboard and ensure no default messages are set. For persistent issues, contacting Vapi support may be necessary, as this behavior may be hardcoded for MCP tools. (Reference: [MCP Integration documentation](https://docs.vapi.ai/tools/mcp)) Source: - [MCP Integration documentation](https://docs.vapi.ai/tools/mcp)

Yeah, this looks like VAPI auto-filling speech while the MCP tool is running, that “isPrecededByText” thing gets added under the hood. Prompts won’t really stop it, so you’re better off forcing silent execution or handling the interim voice response yourself. Also worth checking if the tool call is taking a bit to return. Are your MCP responses fast or lagging a bit? @zackrspv

they are fairly fast, usually 100-400ms

Nice, that’s a clean fix, the space on request-start is a smart way to kill the filler without breaking things. Since your latency is already low, it’s clearly more of a VAPI/TTS behavior than timing. You could push it further by only triggering the delayed message after a short threshold. Have you tried adding a small delay before request-response-delayed fires? @zackrspv

I have not as I’m not sure how lol

Easiest way is to handle it outside Vai, no delay logic built in. Start ~1s timer on MCP call, cancel if it returns fast. Only send delayed message if it exceeds that. That and your setup is the cleanest fix. @zackrspv

Hi, I have a and audio issue that it send back to Vapi on a Spanish number phone. I have been working on this issue for the past 7 days. I really need help. Does anyone has try to set up a ai assistant for Europe using Vapi and telnyx?

Feels like a Telnyx Vapi SIP or codec mismatch, pretty common with EU numbers, so I’d check PCMU/PCMA and make sure audio is flowing both ways, and also confirm nothing is interrupting the stream mid-call, what are you seeing exactly no audio, one-way, or delay? @eytanlevy

@Matt I received a answer from vapi support but no explanation on how to fix it. Root Cause: Codec Mismatch (A-law vs mu-law) Your call to Spain (+34) experienced severe audio quality degradation due to a codec mismatch in Vapi's Telnyx integration. What happened: Spain (and all European countries) use A-law (PCMA) audio encoding on telephony networks Vapi's Telnyx integration hardcodes mu-law (PCMU) decoding for all calls When A-law audio is decoded as mu-law, it produces heavy static/garbled audio The AI couldn't understand the distorted speech → triggered silence-timed-out after 95 seconds

That makes sense, it’s a PCMA (A-law) vs PCMU (mu-law) mismatch, so the fix is to force codec alignment between Telnyx and Vapi. The cleanest workaround is to set your Telnyx SIP connection to transcode everything to PCMU before it hits Vapi, or explicitly prioritize PCMU in the outbound/inbound codec list so Vapi receives the expected format. If transcoding isn’t enabled, you’ll keep getting that garbled audio. If you want, send me a DM and we can hop on a quick call to walk through your Telnyx setup and fix it together. @eytanlevy

@eytanlevy hey there, could you please provide a call id where the MCP tool is being called and saying these predefined messages?

Someone from the community help me

sounds good. let us know if you need anything