What it does

Exposes RetellAI's voice API through 24 MCP tools for building voice applications. Covers call management (create, list, delete phone and web calls), agent provisioning (create voice agents with custom LLM configurations, manage agent versions), phone number management (provision and configure numbers), and voice selection (list and retrieve voice characteristics). Claude can orchestrate complete voice workflows—creating agents, provisioning numbers, initiating calls—without leaving the conversation.

Who it's for

Backend engineers and product teams building voice applications at scale—those provisioning phone numbers, creating LLM-powered agents for customer outreach, and automating phone call workflows without building call infrastructure from scratch.

Common use cases

Create a voice agent with a custom LLM config and initiate an outbound phone call to conduct customer conversations or gather information.
Provision a phone number and assign it to a voice agent for inbound call handling.
List all active calls and agents to monitor the state of a voice application or customer campaign.
Update an agent's LLM configuration (system prompt, model settings) and deploy changes immediately.
Select voice characteristics and apply them to new agents for consistent customer-facing interactions.

Setup pitfalls

Requires a valid RetellAI API key in the RETELL_API_KEY environment variable, available from dashboard.retellai.com/apiKey.
On Claude Desktop, register the server in claude_desktop_config.json with the API key in the env block, then restart the application.
If no tools appear after installation, upgrade to the latest package version: npx -y @abhaybabbar/retellai-mcp-server@latest. Older installs may have dependency mismatches.
Voice agent LLM configuration (model, system prompt) directly affects call behavior. Test agents in a sandbox call before deploying to production customer outreach.

Tool name

Description

Destructive?

list_agents

✓ no

create_agent

✓ no

get_agent

✓ no

update_agent

✓ no

delete_agent⚠

⚠ yes

get_agent_versions		✓ no
create_phone_call		✓ no
create_web_call		✓ no
get_call		✓ no
list_calls		✓ no
update_call		✓ no
delete_call⚠		⚠ yes
list_phone_numbers		✓ no
create_phone_number		✓ no
get_phone_number		✓ no
update_phone_number		✓ no
delete_phone_number⚠		⚠ yes
list_voices		✓ no
get_voice		✓ no
list_retell_llms		✓ no
create_retell_llm		✓ no
get_retell_llm		✓ no
update_retell_llm		✓ no
delete_retell_llm⚠		⚠ yes

@abhaybabbar/retellai-mcp-server

What it does

Who it's for

Common use cases

Setup pitfalls