Built-in Tools

Ultravox Realtime includes several built-in tools that provide common functionality out of the box. These tools are publicly available and work exactly like custom tools you create yourself.

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Available Built-in Tools

More information about these can be found below in Tool Details →

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Using Built-in Tools

Using built-in tools is the same as using any other custom durable tool that you have created except for one difference: you can override built-in tools by using the same name.

For example, if you created a durable tool named “hangUp” and then provide that tool by name (i.e. not by the toolId), then your tool would be used instead of the built-in hangUp tool.

Add built-in tools to your agents when creating calls or call stages:

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Using Tool Names

// Add the hangUp tool by name
{
  "systemPrompt": "You are a helpful assistant. When the conversation naturally concludes, use the 'hangUp' tool to end the call.",
  "selectedTools": [
    { "toolName": "hangUp" }
  ]
}

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Using Tool IDs

If you have multiple tools with the same name, you can use the unique toolId instead. Agents will see the modelToolName.

// Add the hangUp tool by ID (more explicit)
{
  "systemPrompt": "You are a helpful assistant. When the conversation naturally concludes, use the 'hangUp' tool to end the call.",
  "selectedTools": [
    { "toolId": "56294126-5a7d-4948-b67d-3b7e13d55ea7" }
  ]
}

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Viewing Available Tools

Use the List Tools API to see all available tools, including built-ins:

curl -X GET "https://api.ultravox.ai/api/tools" \
  -H "X-API-Key: your-api-key"

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Tool Parameters

Tools can use and pass parameters (i.e. send variables to the underlying API). The parameters for each built-in tool are explained below.

See Tool Parameters → for details about the different types of parameters used by tools.

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Built-in Tool Details

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queryCorpus

Searches through a knowledge base (corpus) to find relevant information (AKA RAG).

Requires the ID of the corpus (corpus_id) to be used for all queries and a dynamic query parameter is used for each query. Optionally, you can restrict the number of results that are returned to the agent (via max_results) along with a minimum semantic similarity score (minimum_score).

Example Usage:

// Basic usage
{
  "selectedTools": [
    {
      "toolName": "queryCorpus",
      "parameterOverrides": {
        "corpusId": "your-corpus-id-here"
      }
    }
  ]
}

// Require semantic similarity of 0.8 or higher
{
  "selectedTools": [
    {
      "toolName": "queryCorpus",
      "parameterOverrides": {
        "corpusId": "your-corpus-id-here",
        "minimum_score": 0.8
      }
    }
  ]
}

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Parameters

Required Parameter Override:

Dynamic Parameters:

Static Parameters:

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leaveVoicemail

When making outbound phone calls, used to leave a voicemail and then end the call.

A dynamic message parameter is used for the message that will be left. Optionally, you can change the hang up behavior with strict and the return message with result.

Example Usage:

// Basic usage
{
  "selectedTools": [
    {
      "toolName": "leaveVoicemail"
    }
  ]
}

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Parameters

Dynamic Parameters:

Static Parameters:

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hangUp

Ends the current call programmatically.

Optionally accepts a dynamic parameter called reason. A static parameter called strict can be overridden to enable the call to continue if the user speaks and continues the call.

Example Usage:

// Basic usage
{
  "systemPrompt": "Help users with their questions. When they say goodbye or the conversation naturally ends, use the hangUp tool to end the call politely.",
  "selectedTools": [
    { "toolName": "hangUp" }
  ]
}

// Enable soft hangup behavior
{
  "selectedTools": [
    {
      "toolName": "hangUp",
      "parameterOverrides": {
        "strict": false
      }
    }
  ]
}

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Parameters

Dynamic Parameters:

Static Parameters:

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playDtmfSounds

Plays telephone keypad tones (dual-tone multi-frequency signals).

Requires a dynamic parameter called digits. Static parameters for toneDuration and spaceDuration can be overridden. Automatically sets the sample rate based on current call medium.

Example:

// Basic usage
{
  "selectedTools": [
    { "toolName": "playDtmfSounds" }
  ]
}

// Increasing length of tones and spaces
{
  "selectedTools": [
    {
      "toolName": "playDtmfSounds",
      "parameterOverrides": {
        "toneDuration": "0.5s",
        "spaceDuration": "0.3s"
      }
    }
  ]
}

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Parameters

Dynamic Parameters:

Static Parameters:

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Customizing Built-in Tools

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Overriding Tool Behavior

You can customize built-in tools by overriding their names or descriptions:

{
  "selectedTools": [
    {
      "toolName": "hangUp",
      "nameOverride": "endConversation",
      "descriptionOverride": "Politely end the conversation when the user is satisfied with the help provided."
    }
  ]
}

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Parameter Overrides

Some built-in tools require or allow parameter overrides:

{
  "selectedTools": [
    {
      "toolName": "queryCorpus",
      "parameterOverrides": {
        "corpusId": "corp-123",
        "maxResults": 5
      }
    }
  ]
}

See the guide on Parameter Overrides →

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Replacing Built-in Tools

You can override built-in tools by creating your own tool with the same name:

// Create a custom "hangUp" tool that logs before ending calls
{
  "name": "hangUp",
  "definition": {
    "modelToolName": "hangUp",
    "description": "Log conversation details and end the call",
    "http": {
      "baseUrlPattern": "https://your-api.com/log-and-hangup",
      "httpMethod": "POST"
    }
  }
}

When you reference a tool by name, your custom tool will be used instead of the built-in version.

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Authentication

Built-in tools handle authentication automatically - no additional setup required. However, some tools like queryCorpus require you to specify which corpus to search via parameter overrides.

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Next Steps

• For more advanced tool usage, see our guides on parameter overrides and async tools.