Integrations · 8 min

Create and Manage Custom Tools for Voice Agents

Custom Tools let a voice agent securely call an external Streamable HTTP MCP server during calls. Create the tool once in the workspace, attach it to the agents that should use it, then remove it from every connected agent before deleting it from the tool catalog.

Walkthrough

Step by step

Prepare the external tool server

Before creating the tool in VZFLO, confirm the external service has an HTTPS Streamable HTTP MCP endpoint and a bearer token that VZFLO can store for authentication.

External MCP server

HTTPS endpointhttps://example.com/mcp Required

Bearer tokenStored by VZFLO and sent securely to the MCP server. Required

Valid tool schemasTool names and input schemas should be compatible with voice agent tool calls. Check

Have the server URL and bearer token ready before creating the tool.

The server should expose clear MCP tool names and schemas so the voice agent knows when and how to call it.

Open Custom Tools

Sign in to VZFLO and open Custom Tools from the app navigation. This page is the reusable tool catalog for the current workspace.

VZFLO / Custom Tools

Tool catalog

Reusable tools for voice agents

Create secure Streamable HTTP MCP tools once, then attach them to voice agents.

Custom Tools

Open Custom Tools from the app navigation.

Create tools here when more than one voice agent may need the same external capability.

Create the custom tool

Enter the tool name, server URL, description, and bearer token, then choose Save custom tool. The description should explain what the tool can do and when the assistant should use it.

VZFLO / Save custom tool

Name bookings_mcp Server URL https://example.com/mcp

Description Retrieve booking details by confirmation number and send messages into a booking thread. Bearer token •••••••••••••••••••••••• Save custom tool

The description tells the assistant what this tool is for.

Example: “This tool retrieves booking details by confirmation number and can send a message into the booking thread.”

Attach the tool to a voice agent

Open Agents, choose the voice agent, find External tool access, and click Edit. In Available tools, choose Attach beside the tool the assistant should be allowed to use.

VZFLO / External tool access

Available tools

bookings_mcphttps://example.com/mcp · Bearer token Attach

On the agent page, open External tool access and attach the tool.

Only attach tools to agents that actually need them. A hotel booking agent may need booking tools, while a sales intake agent may not.

Test the agent

Run a preview call or place a test call. Ask for something that should require the tool, then review the transcript in Analytics or CRM to confirm a tool call appears in the conversation.

VZFLO / Analytics transcript

Assistant

I can help with your booking. What is your confirmation number?

Caller

One two three four five six.

bookings_mcp · get_booking_detailsCompleted successfully

Assistant

I found your booking.

A tool call should appear in the transcript when the assistant uses the external service.

A successful tool call should appear between the caller request and the assistant response that uses the returned information.

Remove the tool from an agent

If an agent should no longer use the tool, return to External tool access on that agent and choose Remove beside the connected tool.

VZFLO / Connected tools

Connected tools

bookings_mcpThis assistant can use the booking MCP server during calls. Remove

Remove the tool from each connected agent before deleting it from the workspace catalog.

Removing a tool from an agent updates that agent’s call configuration without deleting the reusable tool from the workspace catalog.

Delete the custom tool

After the tool has been removed from every connected agent, open Custom Tools and choose Delete on the tool row.

VZFLO / Custom Tools

Tool Server Action

bookings_mcp example.com Delete

Remove this tool from Front Desk before deleting it.

If deletion is blocked, open the named agent and remove the tool first.

VZFLO blocks deletion while the tool is still attached to an agent. If deletion fails, open the named agent, remove the tool, then delete it again from Custom Tools.

Before you finish

Launch checklist

The external MCP server uses HTTPS.
The bearer token is available and valid.
The custom tool has a clear name and description.
The tool is attached only to the voice agents that need it.
A test call shows the tool call in the transcript when expected.
The tool is removed from all agents before deletion.

Fix common issues

Troubleshooting

The custom tool will not save.

Confirm the server URL starts with https://, the bearer token is present, and the external MCP server exposes valid tool schemas.

The agent does not use the tool during a call.

Confirm the tool is attached under External tool access and update the agent instructions so it knows when to use the tool.

The tool cannot be deleted.

The tool is still attached to at least one agent. Open the agent named in the error message, remove the tool under External tool access, then return to Custom Tools and delete it.