Logging

Every tool call and /api/query request is logged by the SqlMcp.Services.QueryService category, so the log is an audit trail of what each agent asked for and what ran.

What a call logs

Each entry names the agent, the database, the SQL (or the schema lookup), the names of any parameters, how long it took, and how many rows came back:

2026-10-18T14:02:11.384Z info: SqlMcp.Services.QueryService[0]
      Ran query with parameters customer: SELECT id FROM orders WHERE customer = @customer on prod for reporting in 12 ms, 3 rows.
2026-10-18T14:02:15.020Z info: SqlMcp.Services.QueryService[0]
      Ran describe_table orders on prod for reporting in 8 ms, 6 rows.
2026-10-18T14:02:40.019Z warn: SqlMcp.Services.QueryService[0]
      Refused query: DELETE FROM orders on prod for reporting: Only SELECT queries (including CTEs) are permitted.

• Parameter values are never logged, only their names.
• The agent is the name its token has in App:AgentTokens. Over stdio, or over HTTP without tokens, it’s unauthenticated.
• explain_query calls are logged as explain, list_tables as list_tables with any schema and search, and list_databases with the number of databases.
• A truncated result is marked (truncated).

Warnings and errors

Level	When
warn	A call refused before it reached the database: unknown database, a statement that isn’t a read, invalid parameters, a missing password variable. The SQL is included, so the log shows what each agent tried as well as what ran.
warn	A call that failed: a database error, a timeout, a busy database, a describe_table that found no table or more than one.
warn	A request with a missing or unknown bearer token, logged by SqlMcp.Http.HttpSecurity with its method, path and remote address, never the token.
fail	A database whose login failed the audit, with each privilege found. Logged when the audit runs, at most every five minutes.

At startup, sql-mcp also warns about databases set to AllowWritableLogin, databases whose password variable isn’t set, and a configuration with no databases.

Levels and format

appsettings.Production.json applies in the Production environment, which is the default when no environment is set, and what the Docker image sets. It keeps QueryService at Information and everything else at Warning, and starts each entry with the UTC time:

{
  "Logging": {
    "LogLevel": {
      "Default": "Warning",
      "Microsoft.AspNetCore": "Warning",
      "SqlMcp.Services.QueryService": "Information"
    },
    "Console": {
      "FormatterName": "simple",
      "FormatterOptions": { "TimestampFormat": "yyyy-MM-ddTHH:mm:ss.fffZ ", "UseUtcTimestamp": true }
    }
  }
}

• To log only refusals and failures, set SqlMcp.Services.QueryService to Warning.
• Under systemd, journald records its own timestamps, so you can drop the timestamp format.

In stdio mode every log line goes to stderr, because stdout carries the MCP stream.