c9d36b04bf
Three pages carried names the 2026-07-28 specification does not use: "Multi-Round-Trip Results" for the pattern the specification titles Multi Round-Trip Requests (MRTR) and serves at basic/patterns/mrtr - the results are the `InputRequiredResult` wire type, not the feature - plus "Completions" for the utility the specification titles Completion, and "Notification Subscriptions" for the pattern it titles Subscriptions. Retitle the three pages to the specification's names, move them to /server/mrtr/ and /client/mrtr/, /server/completion/, and /server/subscriptions/ following the specification's slugs, update every internal reference, and keep the URLs published with v1.3.0 working via jekyll-redirect-from. The Discovery page keeps its title but moves from /server/discovery/ to /server/discover/, matching the specification's slug and the `server/discover` RPC, with its published URL redirected the same way.
90 lines
3.3 KiB
Markdown
90 lines
3.3 KiB
Markdown
---
|
|
layout: default
|
|
title: Logging
|
|
nav_order: 17
|
|
---
|
|
|
|
# Logging
|
|
|
|
The MCP Ruby SDK supports structured logging through the `notify_log_message` method, following the [MCP Logging specification](https://modelcontextprotocol.io/specification/latest/server/utilities/logging).
|
|
|
|
The `notifications/message` notification is used for structured logging between client and server.
|
|
|
|
{: .warning }
|
|
> MCP Logging (`logging/setLevel` and `notifications/message`) is deprecated as of protocol version `2026-07-28` (SEP-2577),
|
|
> while remaining fully supported under `2025-11-25`. Use stderr or OpenTelemetry for new servers.
|
|
|
|
{: .note }
|
|
> On the [modern lifecycle](/server/discover/#the-stateless-modern-lifecycle), where `logging/setLevel` does not exist, the level
|
|
> comes per request from the `io.modelcontextprotocol/logLevel` `_meta` member: it authorizes
|
|
> `notifications/message` for that request only, delivered on the request's own response stream.
|
|
> A request without the member (or with an unrecognized level) receives no log messages.
|
|
|
|
## Log Levels
|
|
|
|
The SDK supports 8 log levels with increasing severity:
|
|
|
|
- `debug` - Detailed debugging information
|
|
- `info` - General informational messages
|
|
- `notice` - Normal but significant events
|
|
- `warning` - Warning conditions
|
|
- `error` - Error conditions
|
|
- `critical` - Critical conditions
|
|
- `alert` - Action must be taken immediately
|
|
- `emergency` - System is unusable
|
|
|
|
## How Logging Works
|
|
|
|
1. **Client Configuration**: The client sends a `logging/setLevel` request to configure the minimum log level
|
|
2. **Server Filtering**: The server only sends log messages at the configured level or higher severity
|
|
3. **Notification Delivery**: Log messages are sent as `notifications/message` to the client
|
|
|
|
For example, if the client sets the level to `"error"` (severity 4), the server will send messages with levels: `error`, `critical`, `alert`, and `emergency`.
|
|
|
|
For more details, see the [MCP Logging specification](https://modelcontextprotocol.io/specification/latest/server/utilities/logging).
|
|
|
|
**Usage Example:**
|
|
|
|
The client first configures the level with a `logging/setLevel` request:
|
|
|
|
```json
|
|
{ "jsonrpc": "2.0", "id": 1, "method": "logging/setLevel", "params": { "level": "info" } }
|
|
```
|
|
|
|
The server then emits messages at each severity; only those at or above the configured level are delivered:
|
|
|
|
```ruby
|
|
server = MCP::Server.new(name: "my_server")
|
|
transport = MCP::Server::Transports::StdioTransport.new(server)
|
|
|
|
server.notify_log_message(
|
|
data: { message: "Application started successfully" },
|
|
level: "info"
|
|
)
|
|
|
|
server.notify_log_message(
|
|
data: { message: "Configuration file not found, using defaults" },
|
|
level: "warning"
|
|
)
|
|
|
|
server.notify_log_message(
|
|
data: {
|
|
error: "Database connection failed",
|
|
details: { host: "localhost", port: 5432 }
|
|
},
|
|
level: "error",
|
|
logger: "DatabaseLogger" # Optional logger name
|
|
)
|
|
```
|
|
|
|
**Key Features:**
|
|
|
|
- Server has capability `logging` to send log messages
|
|
- Messages are only sent if a transport is configured
|
|
- Messages are filtered based on the client's configured log level
|
|
- If the log level hasn't been set by the client, no messages will be sent
|
|
|
|
## Transport Support
|
|
|
|
- **stdio**: Notifications are sent as JSON-RPC 2.0 messages to stdout
|
|
- **Streamable HTTP**: Notifications are sent as JSON-RPC 2.0 messages over HTTP with streaming (chunked transfer or SSE)
|