Merge pull request modelcontextprotocol#30 from modelcontextprotocol/justin/syslog-levels

Use full list of syslog logging severities

Author: jspahrsummers

docs/spec/logging.md

@@ -0,0 +1,177 @@
+---
+title: Logging
+type: docs
+weight: 5
+description: "MCP protocol specification for server logging capabilities"
+---
+
+Logging enables servers to send log messages to clients in a structured way. Clients can control the verbosity of logging by setting the minimum log level they want to receive. Each log message includes a level indicating its severity, an optional logger name for organization, and arbitrary data that can be any JSON-serializable value.
+
+## Capabilities
+
+To indicate support for the Logging API, servers MUST include a `logging` capability in their `ServerCapabilities` during initialization. The `logging` capability SHOULD be an empty object:
+
+```json
+{
+  "capabilities": {
+    "logging": {}
+  }
+}
+```
+
+Clients SHOULD check for this capability before attempting to set the log level.
+
+## Concepts
+
+### Log Levels
+
+MCP defines the following log levels in order of increasing severity:
+
+- `debug`: Detailed information for debugging
+- `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
+
+These levels correspond to syslog severity levels as defined in [RFC 5424](https://datatracker.ietf.org/doc/html/rfc5424#section-6.2.1).
+
+### Log Messages
+
+Each log message contains:
+- A severity level
+- Optional logger name for categorization
+- Arbitrary data payload (any JSON-serializable value)
+
+## Use Cases
+
+Common use cases for logging include:
+
+### Informational Updates
+
+```json
+{
+  "level": "info",
+  "logger": "file_processor",
+  "data": "Processing file: example.txt"
+}
+```
+
+### Transient errors
+
+{
+  "level": "error",
+  "logger": "git_clone",
+  "data": {
+    "error": "Remote repository temporarily unreachable",
+    "details": {
+      "repository": "github.com/example/repo",
+      "attempt": 2,
+      "maxAttempts": 3,
+      "willRetry": true,
+      "retryIn": "5s"
+    }
+  }
+}
+
+## Diagram
+
+The following diagram visualizes the logging interaction between client and server:
+
+```mermaid
+sequenceDiagram
+    participant Client
+    participant Server
+
+    Note over Client,Server: Configure logging
+    Client->>Server: logging/setLevel (info)
+    Server-->>Client: EmptyResult
+
+    Note over Client,Server: Server sends log messages
+    Server--)Client: notifications/message (info)
+    Server--)Client: notifications/message (error)
+```
+
+## Messages
+
+This section defines the protocol messages for logging in the Model Context Protocol (MCP).
+
+### Setting Log Level
+
+#### Request
+
+To configure the minimum log level to receive, the client MUST send a `logging/setLevel` request.
+
+Method: `logging/setLevel`
+Params:
+  - `level`: The minimum severity level of logs to receive (string, required)
+
+Example:
+```json
+{
+  "jsonrpc": "2.0",
+  "id": 1,
+  "method": "logging/setLevel",
+  "params": {
+    "level": "info"
+  }
+}
+```
+
+#### Response
+
+The server MUST respond with an empty result if successful:
+
+```json
+{
+  "jsonrpc": "2.0",
+  "id": 1,
+  "result": {}
+}
+```
+
+### Log Message Notification
+
+The server sends log messages to the client using the `notifications/message` notification.
+
+Method: `notifications/message`
+Params:
+  - `level`: The severity level of the message (string, required)
+  - `logger`: Optional name of the logger (string)
+  - `data`: The log message data (any JSON-serializable value, required)
+
+Example:
+```json
+{
+  "jsonrpc": "2.0",
+  "method": "notifications/message",
+  "params": {
+    "level": "error",
+    "logger": "database",
+    "data": {
+      "error": "Connection failed",
+      "details": {
+        "host": "localhost",
+        "port": 5432
+      }
+    }
+  }
+}
+```
+
+## Error Handling
+
+Clients MUST be prepared to handle:
+- Invalid log levels in setLevel requests
+- Missing or malformed log message parameters
+- Unexpected data types in log messages
+
+## Security Considerations
+
+Implementations MUST carefully consider:
+- Sanitizing sensitive information from log messages
+- Rate limiting log messages to prevent flooding
+- Access control for log configuration
+- Validation of log data to prevent injection attacks

schema/schema.json

@@ -924,11 +924,15 @@
             "type": "object"
         },
         "LoggingLevel": {
-            "description": "The severity of a log message.",
+            "description": "The severity of a log message.\n\nThese map to syslog message severities, as specified in RFC-5424:\nhttps://datatracker.ietf.org/doc/html/rfc5424#section-6.2.1",
             "enum": [
+                "alert",
+                "critical",
                 "debug",
+                "emergency",
                 "error",
                 "info",
+                "notice",
                 "warning"
             ],
             "type": "string"

schema/schema.ts

@@ -659,8 +659,11 @@ export interface LoggingMessageNotification extends Notification {
 
 /**
  * The severity of a log message.
+ * 
+ * These map to syslog message severities, as specified in RFC-5424:
+ * https://datatracker.ietf.org/doc/html/rfc5424#section-6.2.1
  */
-export type LoggingLevel = "debug" | "info" | "warning" | "error";
+export type LoggingLevel = "debug" | "info" | "notice" | "warning" | "error" | "critical" | "alert" | "emergency";
 
 /* Sampling */
 /**