Mcp tools/list empty on prod but working on dev

[AlanCrevon]

Hi all.

When my app is deployed to production, mcp tools are not registered. Everything works as expected in development.

No error in logs. It just fails silently

In dev :

 curl -s "$BASE_URL/_mcp" \
>   -H "Authorization: Bearer $ACCESS_TOKEN" \
>   -H "Mcp-Session-Id: $MCP_SESSION_ID" \
>   -H "Content-Type: application/json" \
>   -d '{
quote>     "jsonrpc": "2.0",
quote>     "method": "tools/list",
quote>     "id": 2
quote>   }' | jq .
{
  "jsonrpc": "2.0",
  "id": 2,
  "result": {
    "tools": [
      {
        "name": "my_tool",
        "title": "Test tool",
        "inputSchema": {
          "type": "object",
          "properties": {}
        },
        "description": "test tool"
      }
    ]
  }
}

In prod :

 curl -s "$BASE_URL/_mcp" \
>   -H "Authorization: Bearer $ACCESS_TOKEN" \
>   -H "Mcp-Session-Id: $MCP_SESSION_ID" \
>   -H "Content-Type: application/json" \
>   -d '{
quote>     "jsonrpc": "2.0",
quote>     "method": "tools/list",
quote>     "id": 2
quote>   }' | jq .
{
  "jsonrpc": "2.0",
  "id": 2,
  "result": {
    "tools": []
  }
}

mcp.yaml

mcp:
  app: 'apelia'
  version: '1.0.0'
  description: 'MCP server for Apelia.'
  pagination_limit: 50
  instructions: 'MCP server for Apelia application tools and resources.'

  client_transports:
    stdio: false
    http: true

  http:
    path: /_mcp
    session:
      store: file
      directory: '%kernel.cache_dir%/mcp-sessions'
      ttl: 3600

ai:
    platform:
        # Inference Platform configuration
        # see https://github.com/symfony/ai/tree/main/src/platform#platform-bridges

        # openai:
        #    api_key: '%env(OPENAI_API_KEY)%'

    agent:
        # Agent configuration
        # see https://symfony.com/doc/current/ai/bundles/ai-bundle.html

        # default:
        #    platform: 'ai.platform.openai'
        #    model: 'gpt-5-mini'
        #    prompt: |
        #        You are a pirate and you write funny.
        #    tools:
        #        - 'Symfony\AI\Agent\Bridge\Clock\Clock'

    store:
        # Store configuration

        # chromadb:
        #    default:
        #        client: 'client.service.id'
        #        collection: 'my_collection'

• php 8.3
• Symfony 7.4
• "symfony/mcp-bundle": "*", (v0.9.0 installed)
• "symfony/ai-bundle": "*", (v0.9.0 installed)

What information should i provide to help ?

[OskarStark]

Hi @AlanCrevon, thanks for the report.

The bundle discovers tools through two parallel mechanisms, and they behave a bit differently between dev and prod:

1. Compile-time, via the #[McpTool] attribute → mcp.tool tag → a ServiceLocator built by McpPass. This requires the tool class to be registered as a service with autoconfigure enabled.
2. Runtime filesystem discovery, via setDiscovery($projectDir, scan_dirs, exclude_dirs). scan_dirs defaults to ['src'].

A few things to check that would help us narrow it down:

• After your latest deploy, did you run bin/console cache:clear --env=prod (and cache:warmup)? The discovery result is cached, so a stale prod cache will show up as an empty tools list with no errors.
• Output of bin/console debug:container --tag=mcp.tool --env=prod — does the tag appear after the container is compiled for prod?
• Where does your tool class live relative to scan_dirs: ['src']? If it's outside src/, runtime discovery will miss it.
• Is var/cache/prod/mcp-sessions writable by the web server user? Your config uses session.store: file under %kernel.cache_dir%, and the cache dir differs between dev (var/cache/dev) and prod (var/cache/prod).
• The \$MCP_SESSION_ID you're sending — was it obtained from an initialize call against the prod endpoint? A session id from dev won't exist in prod's session store, and an uninitialized session can produce an empty capabilities response rather than an error.

If you can share the output of debug:container --tag=mcp.tool --env=prod and confirm a fresh initialize was done against prod, that should pin it down quickly.