GoHighLevel MCP Server (Self-Hosted)

Use case: Connect AI apps like RetellAI and Vapi directly to GoHighLevel (GHL) for contact + booking workflows. This project may also work with other MCP-compatible apps.

No middleware required: direct RetellAI/Vapi -> GHL integration without apps like n8n or make.com.

If this is your first time using Vercel or MCP, setup typically takes 15-30 minutes.

You maybe asking why not just use GHL's native MCP? At the time of development they do not provide tooling for querying calendars for open slots or booking appointments.

Table of Contents

• What This Server Does

• Quick Start Checklist

• 1. Deploy on Vercel

• 2. Connect MCP in Your Agent Platform

• 3. Recommended Agent Flow

• 4. Troubleshooting

Related MCP server: GoHighLevel MCP Server

What This Server Does

• Create or update contacts (ghl_create_contact)

• Search contacts (ghl_search_contacts)

• Retrieve calendar free slots (ghl_get_calendar_free_slots)

• Create confirmed appointments (ghl_create_appointment)

Endpoint:

• POST /mcp

Quick Start Checklist

• Deploy this repo to Vercel

• Add required environment variables

• Copy your Vercel /mcp URL

• Add MCP in RetellAI with required headers

• Add all 4 tools to your Retell agent

• Run one end-to-end test call

1. Deploy on Vercel

1.1 Import this repo

1. Go to Vercel.

2. Create a new project.

3. Import this GitHub repository.

4. Deploy.

1.2 Add environment variables

In Vercel project settings, add the following:

Private Integration scopes required:

• contacts.readonly

• contacts.write

• calendars.readonly

• calendars/events.write

Hardcoded in app (no env needed):

• GHL base URL: https://services.leadconnectorhq.com

• GHL API version header: 2021-07-28

1.3 Confirm endpoint

Your MCP URL will be:

• https://<your-vercel-domain>/mcp

2. Connect MCP in Your Agent Platform

Choose one platform below. RetellAI and Vapi are separate alternatives. This MCP server may also work with other MCP-capable platforms, but testing for this project was conducted using RetellAI and Vapi.

Option A: RetellAI

2.1 Add MCP (matches Retell UI)

In RetellAI -> Add MCP:

• Name: GHL MCP (or any label)

• URL: https://<your-vercel-domain>/mcp

• Timeout (ms): 10000

Under Headers, add:

• Authorization = Bearer <GHL_PRIVATE_INTEGRATION_TOKEN>

• locationId = <DEFAULT_LOCATION_ID>

• X-MCP-KEY = <MCP_SHARED_SECRET>

• calendarId = <GHL_CALENDAR_ID>

Under Query Parameters:

• leave empty

Then click Save.

2.2 Add tools to your agent

In RetellAI -> Add Tool, add:

1. ghl_create_contact

2. ghl_search_contacts

3. ghl_get_calendar_free_slots

4. ghl_create_appointment

Recommended toggles:

• Speak During Execution: off

• Speak After Execution: on

Optional variable mapping:

• Store ghl_create_contact.contactId as contact_id

• Use contact_id for ghl_create_appointment.contactId

Important notes:

• calendarId header is required for calendar tools.

• X-MCP-KEY must exactly match your Vercel MCP_SHARED_SECRET.

• Get calendarId from GHL calendar settings.

Option B: Vapi

2.3 Create the MCP tool

In Vapi:

1. Go to Tools (left menu).

2. Click Create Tool.

3. Select MCP.

Configure these fields:

• Tool Name: ghl_mcp (or any label)

• Description: GHL MCP

• Server URL: https://<your-vercel-domain>/mcp

• Timeout: 20 seconds (recommended)

Under HTTP Headers, add:

• Authorization = Bearer <GHL_PRIVATE_INTEGRATION_TOKEN>

• locationId = <DEFAULT_LOCATION_ID>

• X-MCP-KEY = <MCP_SHARED_SECRET>

• calendarId = <GHL_CALENDAR_ID>

Under MCP Settings:

• Select Streamable HTTP (SHTTP) (recommended)

• SSE is also supported if needed

Then click Save.

2.4 Assign the MCP tool to your assistant

After saving the MCP tool:

1. Go to Assistants.

2. Select your assistant.

3. Open the Tools dropdown/menu.

4. Assign the MCP tool you created.

Important:

• If the tool is not assigned to the assistant, calls will not use this MCP server.

• X-MCP-KEY must match your Vercel MCP_SHARED_SECRET exactly.

• calendarId header is required for calendar tools.

3. Recommended Agent Flow

1. ghl_search_contacts

2. ghl_create_contact (only if no match)

3. ghl_get_calendar_free_slots

4. ghl_create_appointment

Copy/Paste system prompt tool policy

Use this in your Retell system prompt. You can customize it, but test with real calls before production.

Use MCP tools for all contact + booking actions.
Do not invent contact IDs, availability, or confirmations.
Never mention tool names, tool calls, or internal MCP/tool errors to the caller.

Flow:
1) Run ghl_search_contacts first using available phone/email/query.
2) If exactly one contact is found, use that contactId.
3) If no contact is found, collect missing phone/email and run ghl_create_contact.
4) If multiple contacts are found, disambiguate before booking.
5) Run ghl_get_calendar_free_slots and only offer returned slots.
6) Run ghl_create_appointment only with a confirmed contactId and an offered slot.

If no slots, ask for a different date range.
If tool error, say there is a technical issue and retry or escalate.
Confirm booking only after ghl_create_appointment succeeds.

4. Troubleshooting

• 401 AUTH_ERROR: a required header is missing or invalid.

• 403 location access error: verify token access and locationId.

• Empty free slots:

  • verify calendarId header

  • verify date range + timezone

  • verify calendar availability in GHL