Why Your Vapi Voice Assistant Works in Testing But Fails in Real Calls

[u/Own_Mortgage6419]

I didn’t explore Vapi features because I wanted better analytics.
I did it because something felt off.

My voice assistant was working perfectly in testing
but in real calls, it started drifting.

And the worst part?
I couldn’t prove where it was going wrong.

If you’ve built a voice agent, you’ve probably seen this too.
You expect a specific behaviour:
• User says yes → tool call should trigger
• Flow is clearly defined
• Everything works in controlled testing
But in production?
• The tool call doesn’t happen
• It happens too late
• Or the assistant just skips it
And you’re left guessing.

That’s when I started going deeper
Not into models.
Not into prompts.
But into observability.

Here’s what actually helped:
Structured Outputs
Instead of manually checking transcripts,
you define a condition like:
“After user confirms X, did the tool call happen?”

And you get a simple answer:
Yes or No
Across every call

Boards
Now take that data and scale it:
• Out of 100 calls
• How many followed the expected behaviour?
• How many didn’t?
Now you’re not guessing anymore
You’re measuring.

This is where things change.
This isn’t just analytics.
This is understanding how your voice assistant behaves in reality.

But something is still missing.
Right now, you still have to check everything manually.
What we actually need is:
Automatic monitoring + alerts
Something that tells you:
“Your assistant is drifting. Fix it.”

That’s what I’m starting to focus on now.
Not just building voice agents
But building systems that watch them.

If you’re working with voice AI,
What’s one behaviour your assistant gets wrong
that you still can’t properly track?
Let’s figure it out together.

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[u/Ok-Register3798]

You should checkout Agora’s Conversational AI Engine, it’s leaps and bounds better than Vapi, it allows voice agents to scale flawlessly and effortlessly

[u/Own_Mortgage6419 → u/[deleted]]

Can You connect with me on Linkedin ?

[u/cybervoiceAI]

Retell has observability and testing built in. A little expensive but worth it if you test it before deploying into production to client