Environment Variables

mcserial reads configuration from environment variables at startup. These variables set server-wide defaults that apply to all connections unless overridden by tool parameters.

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Server Configuration

MCSERIAL_DEFAULT_BAUDRATE

Default baud rate used when open_serial_port is called without a baudrate parameter and auto-detection either fails or is not applicable (e.g., URL-based connections).

Default	9600
Type	Integer
Example	MCSERIAL_DEFAULT_BAUDRATE=115200

# Set a higher default for modern devices
export MCSERIAL_DEFAULT_BAUDRATE=115200

MCSERIAL_DEFAULT_TIMEOUT

Default read timeout in seconds for new connections. Applied as the timeout parameter when open_serial_port is called without an explicit timeout.

Default	1.0
Type	Float (seconds)
Example	MCSERIAL_DEFAULT_TIMEOUT=2.0

# Longer timeout for slow devices
export MCSERIAL_DEFAULT_TIMEOUT=5.0

MCSERIAL_MAX_CONNECTIONS

Maximum number of simultaneously open serial port connections. Attempts to open more ports than this limit return an error.

Default	10
Type	Integer
Example	MCSERIAL_MAX_CONNECTIONS=20

# Allow more concurrent connections
export MCSERIAL_MAX_CONNECTIONS=20

Note

Each open connection holds a file descriptor and kernel buffer memory. The default of 10 is sufficient for most use cases. Increase it only if you genuinely need many simultaneous connections.

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Setting Environment Variables

Tip

When using mcserial with Claude Code, set environment variables before adding the server:

# Option 1: Inline with the command
claude mcp add mcserial "env MCSERIAL_DEFAULT_BAUDRATE=115200 uvx mcserial"

# Option 2: Export in your shell profile
export MCSERIAL_DEFAULT_BAUDRATE=115200
claude mcp add mcserial "uvx mcserial"

For other MCP clients, consult their documentation for how to pass environment variables to server processes.

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Installation Extras

mcserial supports optional dependency groups for specialized hardware.

mcserial[cp2110]

Adds the hidapi package for Silicon Labs CP2110 HID-to-UART bridge support. Required to use the cp2110:// URL scheme with open_serial_port.

# Install with CP2110 support
uv pip install mcserial[cp2110]

# Or with uvx
uvx --with hidapi mcserial

Without this extra installed, attempting to open a cp2110:// URL returns an error:

cp2110:// requires the hidapi package. Install with: pip install mcserial[cp2110]

Note

The hidapi package has system-level dependencies on some platforms. On Linux, you may need libhidapi-dev or equivalent. On macOS, it installs cleanly via pip. On Windows, no additional system packages are needed.