feat: add multi-host support for connecting to multiple SQL Servers

README.md

@@ -16,6 +16,7 @@ A Model Context Protocol (MCP) server for secure SQL Server database access thro
 - 🔐 Multiple authentication methods (SQL, Windows, Azure AD)
 - 🏢 LocalDB and Azure SQL support
 - 🔌 Custom port configuration
+- 🌐 **Multi-host support** — connect to multiple SQL Servers from a single MCP instance
 
 ## Quick Start
 
@@ -72,6 +73,119 @@ MSSQL_PORT=1433                 # Custom port (default: 1433)
 MSSQL_ENCRYPT=true              # Force encryption
 ```
 
+### Multi-Host Configuration
+
+Connect to **multiple SQL Servers** from a single MCP server instance. Each
+connection has its own name, credentials, and settings.
+
+When multi-host mode is active the `execute_sql` tool gains a required
+`connection` parameter, and a new `list_connections` tool becomes available.
+
+#### Option 1 — Indexed environment variables (recommended)
+
+Define hosts with `MSSQL_HOST_<N>_*` env vars. Each index is a separate
+connection:
+
+```json
+{
+  "mcpServers": {
+    "mssql": {
+      "command": "uvx",
+      "args": ["microsoft_sql_server_mcp"],
+      "env": {
+        "MSSQL_HOST_1_NAME": "prod",
+        "MSSQL_HOST_1_SERVER": "prod.example.com",
+        "MSSQL_HOST_1_DATABASE": "proddb",
+        "MSSQL_HOST_1_USER": "admin",
+        "MSSQL_HOST_1_PASSWORD": "secret",
+
+        "MSSQL_HOST_2_NAME": "dev",
+        "MSSQL_HOST_2_SERVER": "dev.example.com",
+        "MSSQL_HOST_2_DATABASE": "devdb",
+        "MSSQL_HOST_2_USER": "dev",
+        "MSSQL_HOST_2_PASSWORD": "devpass",
+        "MSSQL_HOST_2_PORT": "1434"
+      }
+    }
+  }
+}
+```
+
+Indexes don't have to be contiguous — `1, 2, 5, 10` works fine.
+
+#### Option 2 — JSON config file
+
+Point `MSSQL_CONNECTIONS_FILE` to a JSON file on disk:
+
+```json
+{
+  "mcpServers": {
+    "mssql": {
+      "command": "uvx",
+      "args": ["microsoft_sql_server_mcp"],
+      "env": {
+        "MSSQL_CONNECTIONS_FILE": "/path/to/connections.json"
+      }
+    }
+  }
+}
+```
+
+Where `connections.json` looks like:
+
+```json
+[
+  {
+    "name": "prod",
+    "server": "prod.example.com",
+    "database": "proddb",
+    "user": "admin",
+    "password": "secret"
+  },
+  {
+    "name": "dev",
+    "server": "dev.example.com",
+    "database": "devdb",
+    "user": "dev",
+    "password": "devpass",
+    "port": "1434"
+  },
+  {
+    "name": "local",
+    "server": "localhost",
+    "database": "localdb",
+    "windows_auth": "true"
+  }
+]
+```
+
+#### Connection fields
+
+Each host supports these fields (as env var suffixes or JSON keys):
+
+| Field / Suffix   | Required | Default     | Description                              |
+|------------------|----------|-------------|------------------------------------------|
+| `NAME`           | Yes      | —           | Unique connection identifier             |
+| `SERVER`         | No       | `localhost` | SQL Server hostname                      |
+| `DATABASE`       | Yes      | —           | Database name                            |
+| `USER`           | Cond.    | —           | Username (required for SQL auth)         |
+| `PASSWORD`       | Cond.    | —           | Password (required for SQL auth)         |
+| `PORT`           | No       | `1433`      | TCP port                                 |
+| `ENCRYPT`        | No       | `false`     | Enable encryption (`true`/`false`)       |
+| `WINDOWS_AUTH`   | No       | `false`     | Use Windows authentication               |
+
+#### Resolution order
+
+1. `MSSQL_HOST_<N>_*` env vars (highest priority)
+2. `MSSQL_CONNECTIONS_FILE` JSON file
+3. Legacy single-host env vars (`MSSQL_SERVER`, `MSSQL_USER`, etc.)
+
+#### Backward compatibility
+
+If no `MSSQL_HOST_*` env vars or `MSSQL_CONNECTIONS_FILE` are set, the server
+falls back to the original single-host environment variables — **no changes
+needed for existing setups**.
+
 ## Alternative Installation Methods
 
 ### Using pip