QA for your Vapi agents
Vapi tells you a call happened. Zelto tells you whether it went well — and exactly what to fix when it didn't. Paste an API key and Zelto pulls your assistants and calls automatically.
What actually breaks on Vapi in production
Dashboards show you that calls happened. They don't show you the calls that quietly failed — and those are the ones that cost you customers.
Tool calls that fail silently
A webhook times out or returns an error mid-conversation, and the assistant talks right past it. The caller hears confidence; your CRM never gets the update. Zelto flags every call where a tool call failed and the agent didn't recover.
Squad transfers that go sideways
Multi-assistant squads hand calls to the wrong assistant, or drop context at the handoff. These failures never show up in latency dashboards — they only show up in what was actually said.
Prompt updates that regress old flows
You tweak the system prompt to fix one behavior and quietly break three others. Zelto grades every call after the change, so the regression surfaces as a Finding within hours, not after a customer complains.
Callers stuck in dead ends
Interruptions mishandled, questions the assistant can't answer, loops the caller can't escape. Individually they look like one-off bad calls. Zelto clusters them, so 40 calls hitting the same dead end become one ranked Finding.
How Zelto works with Vapi
Connect
Paste your Vapi API key. Zelto pulls your assistants and starts ingesting calls automatically — recordings, transcripts, tool calls, and metadata. No code changes to your agent.
Zelto listens and diagnoses
Every production call is graded against a rubric Zelto auto-learns from your traffic — your domain, your language, your definition of a good call. No setup, no scorecard to write.
Findings, with the fix drafted
Calls that fail for the same reason are clustered into one Finding, ranked by volume, with example calls, a drafted prompt fix, Slack alerts, and an optional Linear ticket.
Production traffic, not simulations.
Simulation tools grade synthetic conversations against scenarios you wrote. Zelto grades what actually happened with real callers on your Vapiagents — because that's where the failures that matter live. Most teams are integrated in under 15 minutes.
Zelto + Vapi
The questions teams ask before connecting. Answered honestly.
Other integrations
One week. One agent. Ten findings
Connect one production agent. Zelto listens, then walks you through ten findings with severity, examples, and fixes.
Book a demo