Overview

Global Configuration

Precedence

The order of precedence for these options is: CLI flag > environment variable > default value

Config File Path

All commands support an optional parameter to specify the location of the mcpd config file.

You can provide this path in multiple ways:

• CLI flag: --config-file <path>
• Environment variable: MCPD_CONFIG_FILE=<path>
• Default: .mcpd.toml in the current working directory

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Sample Configuration File

[[servers]]
  name = "fetch"
  package = "uvx::mcp-server-fetch@2025.4.7"
  tools = ["fetch"]

[[servers]]
  name = "time"
  package = "uvx::mcp-server-time@2025.8.4"
  tools = ["get_current_time", "convert_time"]

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Log Level

Sets the logging level for mcpd.

You can configure it using:

• CLI flag: --log-level=<level>
• Environment variable: MCPD_LOG_LEVEL=<level>

Default:

INFO

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Log Path

Sets the log file path for mcpd.

Options:

• CLI flag: --log-path=<path>
• Environment variable: MCPD_LOG_PATH=<path>

Setting Log Path

Log entries will be discarded by default, unless a log path is configured. Output intended for the terminal is still emitted.

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Hot Reload

The mcpd daemon supports hot-reloading of MCP server configurations without requiring a full restart. This allows you to add, remove, or modify server configurations while keeping the daemon running.

Hot reload processes both:

• Server configuration (--config-file) e.g. .mcpd.toml
• Execution context (--runtime-file) e.g. secrets.dev.toml

SIGHUP Signal

Send a SIGHUP signal to the running daemon process to trigger a configuration reload:

# Find the daemon process ID
ps aux | grep mcpd

# Send reload signal (replace PID with actual process ID)
kill -HUP <PID>

Reload Behavior

During a hot reload, the daemon intelligently categorizes changes and responds accordingly:

Change Type	Action	Description
Unchanged servers	Preserve	Servers with identical configurations keep their existing connections, tools, and health status
Removed servers	Stop	Servers no longer in the config file are gracefully shut down
New servers	Start	Newly added servers are initialized and connected
'Tools-Only' changes	Update	When only the tools change, the daemon updates the allowed tools without restarting the server process
Configuration changes	Restart	Servers with other configuration changes (package version, environment variables, arguments, execution context, etc.) are stopped and restarted with new settings

Example: 'Tools-Only' Update

Consider this server configuration:

[[servers]]
  name = "github"
  package = "uvx::modelcontextprotocol/github-server@1.2.3"
  tools = ["create_repository", "get_repository"]

If you modify only the tools list:

[[servers]]
  name = "github" 
  package = "uvx::modelcontextprotocol/github-server@1.2.3"
  tools = ["create_repository", "get_repository", "list_repositories"] # Additional tools

The daemon will:

1. Detect that only the tools array changed
2. Update the allowed tools list in-place
3. Keep the existing server process and connections intact
4. Log a message that tools for a server were updated (including the server name and list of tools)

Example: Package Version Update

If you change the package version:

[[servers]]
  name = "github"
  package = "uvx::modelcontextprotocol/github-server@1.3.0"  # Version changed
  tools = ["create_repository", "get_repository", "list_repositories"]

The daemon will:

1. Detect configuration changes beyond just tools
2. Gracefully stop the existing server
3. Start a new server with the updated configuration
4. Log a message that the server is being restarted (including the server name)

Execution Context and Environment Variables

Environment Variable Visibility

The mcpd process can only see environment variables that existed when it started.

If you export new environment variables in your shell after starting mcpd, you must restart the daemon for those variables to become available for shell expansion.

When the execution context file is reloaded, shell expansion of environment variables (${VAR} syntax) occurs using the environment available to the running mcpd process when it was started.

What Works During Hot Reload

Direct values are applied immediately:

[servers.jira]
  args = ["--confluence-token=test123", "--confluence-url=http://jira-test.mozilla.ai"]
[servers.mcp-discord.env]
  DISCORD_TOKEN = "qwerty123!1one"

Shell expansion of existing environment variables works:

[servers.myserver]
  args = ["--home=${HOME}", "--user=${USER}"]  # These expand to current values
[servers.myserver.env]
  CONFIG_PATH = "${HOME}/.config/myapp"  # Expands using mcpd's environment

What Requires an mcpd Restart

New environment variables added to the system after mcpd started won't be visible:

[servers.myserver]
  args = ["--token=${NEW_TOKEN}"]  # NEW_TOKEN added after mcpd started
[servers.myserver.env]
  API_KEY = "${NEWLY_EXPORTED_VAR}"  # Won't expand until mcpd restarts

Limitations

Hot reload does NOT apply to:

• Daemon-level config settings (timeouts, CORS, etc.)
• New environment variables added to the system

Both require mcpd to be restarted for changes to take effect

Error Handling

The reload process maintains strict consistency - any error causes the daemon to exit:

• Configuration errors: Invalid configuration files or loading failures cause the daemon to exit
• Validation errors: Invalid server configurations cause the daemon to exit
• No tools configured: If a server configuration has no tools (empty tools list or manually removed from config), the daemon will exit with an error
• Server operation failures: Any failure to start, stop, or restart a server causes the daemon to exit

This ensures the daemon never runs in an inconsistent or partially-failed state, matching the behavior during initial startup where any server failure prevents the daemon from running.

Reload Failures

Unlike some systems that allow partial reloads, mcpd exits on any reload error to prevent inconsistent state. You'll need to fix the configuration and restart the daemon.

Diagnosing reload issues

If a change did not take effect, or the daemon exited during reload, see Troubleshooting.

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Configuration Export

The mcpd config export command generates portable configuration files for deployment across different environments. It creates template variables using the naming pattern MCPD__{SERVER_NAME}__{VARIABLE_NAME}.

Template Variable Generation

Environment variables and command-line arguments are both converted to template variables using the same naming scheme:

• Environment variableDATABASE_URL becomes MCPD__{SERVER_NAME}__DATABASE_URL
• Command-line argument --database-url becomes MCPD__{SERVER_NAME}__DATABASE_URL

Variable Name Collisions

Naming Collisions

If a server has both an environment variable and a command-line argument that normalize to the same name (e.g., DATABASE_URL and --database-url), they will generate the same template variable name.

In most cases, this is intentional, the same configuration value is being used in different ways. The collision results in a single template variable that can be used for both the environment variable and command-line argument.

Example Collision

[[servers]]
name = "example"
required_env = ["DATABASE_URL"]
required_args = ["--database-url"]

Both will use the template variable MCPD__EXAMPLE__DATABASE_URL in the generated files.