Symfony Streamable HTTP MCP server

⚠️ Warning: Do not use this in production

This experiment connects ChatGPT to a (local) Symfony application.

Most online examples use an STDIO-based MCP server through console commands. Which works fine locally. This setup embeds the MCP server in an existing web application and makes it accessible online, without running it as a separate process.

MCP Bundle

See MCP Bundle for more information.

Since there is no official release yet, install the dependencies manually:

composer require mcp/sdk@dev-main
composer require symfony/mcp-sdk@dev-main
composer require symfony/mcp-bundle@dev-main

To get this working I had to do some extras.

Add the MCP route

# config/routes.yaml
mcp:
  type: mcp
  resource: .

Configure MCP

# config/packages/mcp.yaml
mcp:
  client_transports:
    http: true
    stdio: false
  discovery:
    scan_dirs:
      - 'src/Mcp'
  http:
    path: '/mcp'

This enables Streamable HTTP. scans tools, prompts, … in src/Mcp. Makes route for the MCP server /mcp.

Firewall

If you’re using a firewall, exclude the MCP route from authentication.
Important: this is insecure! Add proper security if you’re running beyond a local experiment.

Create the MCP Elements

See MCP PHP SDK for more information.

#[McpPrompt(
  name: 'summarize',
  description: 'Gives a prompt to summarize a project.'
)]
public function summarize(string $id): array
{
  return [
    'role' => 'user',
    'content' => "...",
  ];
}

#[McpTool(
  name: 'fetch_project',
  description: 'Fetch a project by the given id.'
)]
public function fetchProject(string $id): string
{
  ...
}

Running MCP Inspector

Most tutorials suggest using MCP Inspector. It was a hassle to get it working with a local web application.

NODE_TLS_REJECT_UNAUTHORIZED='0' npx @modelcontextprotocol/inspector --transport http --server-url https://127.0.0.1:8000/mcp

• NODE_TLS_REJECT_UNAUTHORIZED='0' disables TLS check (needed for self-signed certs, that are use in Symfony Server)
• --transport http enables Transport Type = Streamable HTTP.
• --server-url https://127.0.0.1:8000/mcp points to your local MCP server.
  Use the IP, not the friendly URL if you are using Symfony’s proxy.

After launching the Inspector, confirm that Connection Type shows “Via Proxy”—otherwise it won’t work.

Connecting ChatGPT

ngrok

Use ngrok to expose your local web application to the internet.

ngrok http 8000

Connector in ChatGPT

1. Open ChatGPT.
2. Click your user in the bottom left.
3. Click Settings.
4. Choose “Apps & Connectors”.
   There you can create a new connector.

Use your ngrok url as the MCP Server url. Don’t forget to append /mcp

Select “No authentication”.
As said before: Do not use this on production!

To be able to use the connector without publishing you need to scroll down in the “Apps & Connectors” screen and enable “Developer mode”, under “Advanced settings”.

After enabling developer mode: Activate the tools when chatting with ChatGPT.

If ChatGPT chooses to use your tool, it first asks for permission. Once granted, it immediately calls the tool.