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Retell AI MCP Server

by itsanamune
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JavaScript
Remote

retell_update_agent

Modify settings for an existing voice agent, including voice, language, webhook, and interaction parameters, to adjust its behavior and configuration.

Instructions

Update configuration for an existing voice agent.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
agent_idYesThe agent ID to update
agent_nameNoNew display name
voice_idNoNew voice ID
languageNoNew language code
webhook_urlNoNew webhook URL
interruption_sensitivityNoNew interruption sensitivity
enable_backchannelNoEnable/disable backchannel

Implementation Reference

  • src/index.ts:1175-1178 (handler)
    Handler implementation for the retell_update_agent tool. Extracts agent_id from arguments and sends a PATCH request to the Retell API's /update-agent/{agent_id} endpoint with the remaining update data.
    case "retell_update_agent": {
  const { agent_id, ...agentUpdateData } = args;
  return retellRequest(`/update-agent/${agent_id}`, "PATCH", agentUpdateData as Record<string, unknown>);
}
  • src/index.ts:529-562 (schema)
    Input schema defining the parameters for the retell_update_agent tool, requiring agent_id and allowing optional updates to agent_name, voice_id, language, webhook_url, interruption_sensitivity, and enable_backchannel.
    inputSchema: {
  type: "object",
  properties: {
    agent_id: {
      type: "string",
      description: "The agent ID to update"
    },
    agent_name: {
      type: "string",
      description: "New display name"
    },
    voice_id: {
      type: "string",
      description: "New voice ID"
    },
    language: {
      type: "string",
      description: "New language code"
    },
    webhook_url: {
      type: "string",
      description: "New webhook URL"
    },
    interruption_sensitivity: {
      type: "number",
      description: "New interruption sensitivity"
    },
    enable_backchannel: {
      type: "boolean",
      description: "Enable/disable backchannel"
    }
  },
  required: ["agent_id"]
}
  • src/index.ts:526-563 (registration)
    Tool registration in the tools array used by ListToolsRequestHandler, defining the name, description, and input schema for retell_update_agent.
    {
  name: "retell_update_agent",
  description: "Update configuration for an existing voice agent.",
  inputSchema: {
    type: "object",
    properties: {
      agent_id: {
        type: "string",
        description: "The agent ID to update"
      },
      agent_name: {
        type: "string",
        description: "New display name"
      },
      voice_id: {
        type: "string",
        description: "New voice ID"
      },
      language: {
        type: "string",
        description: "New language code"
      },
      webhook_url: {
        type: "string",
        description: "New webhook URL"
      },
      interruption_sensitivity: {
        type: "number",
        description: "New interruption sensitivity"
      },
      enable_backchannel: {
        type: "boolean",
        description: "Enable/disable backchannel"
      }
    },
    required: ["agent_id"]
  }
},

Tool Definition Quality

C2.9/5.0
Behavior2/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations provided, the description carries full burden but offers minimal behavioral insight. It states this is an update operation (implying mutation) but doesn't disclose permission requirements, whether changes are reversible, rate limits, error conditions, or what happens to unspecified fields. For a mutation tool with zero annotation coverage, this leaves critical behavioral aspects undocumented.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single, efficient sentence that directly states the tool's purpose without unnecessary words. It's appropriately sized for a straightforward update operation and is front-loaded with the essential information. Every word earns its place.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness2/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a mutation tool with 7 parameters, no annotations, and no output schema, the description is insufficiently complete. It doesn't explain what 'configuration' entails beyond the parameter list, doesn't describe the update behavior (partial vs. full updates), and provides no information about return values or error handling. The agent lacks critical context for proper tool invocation.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The schema description coverage is 100%, so all parameters are documented in the schema itself. The description adds no additional parameter semantics beyond what's already in the schema descriptions. This meets the baseline of 3 since the schema does the heavy lifting, but the description doesn't enhance understanding of parameter relationships or constraints.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the action ('Update configuration') and resource ('existing voice agent'), making the purpose immediately understandable. It distinguishes this from creation tools like 'retell_create_agent' by specifying 'existing', but doesn't explicitly differentiate from other update tools like 'retell_update_chat_agent' or 'retell_update_llm' beyond the resource type.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines2/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description provides no guidance on when to use this tool versus alternatives. It doesn't mention prerequisites (e.g., needing an existing agent), when not to use it, or how it differs from other update tools for different resource types. The agent must infer usage from the tool name and sibling list alone.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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