How to Configure the Server Port and Environment Variables in castrozan/tcc

The MCP OpenAPI Server in the castrozan/tcc repository configures the server port and environment variables through the loadConfig() function in mcp-openapi-server/src/config.ts, where command-line arguments take precedence over environment variables, defaulting to port 3000 for HTTP transport.

The castrozan/tcc repository provides an MCP (Model Context Protocol) OpenAPI Server that bridges REST APIs with MCP-compatible clients. Configuring the server port and environment variables correctly is essential for production deployments and local development. This guide explains how the configuration system works based on the actual implementation in mcp-openapi-server/src/config.ts and mcp-openapi-server/src/index.ts.

Configuration Architecture and Priority

The configuration system uses a layered approach defined in mcp-openapi-server/src/config.ts. The loadConfig() function parses inputs using yargs and resolves final values based on strict precedence rules.

Priority order (highest to lowest):

1. Command-line arguments
2. Environment variables
3. Default values

This means a --port flag overrides the HTTP_PORT environment variable, which in turn overrides the default value of 3000.

Configuring the Server Port and Host

When using HTTP transport, three key parameters control network binding: port, host, and endpoint path. These are resolved in loadConfig() at lines 143-145 of mcp-openapi-server/src/config.ts.

Using Command-Line Arguments

Pass flags directly when starting the server:

npx ts-node ./mcp-openapi-server/src/index.ts \
  --transport http \
  --port 8080 \
  --host 0.0.0.0 \
  --path /api/v1/mcp

Using Environment Variables

Set variables in your shell or .env file:

export TRANSPORT_TYPE=http
export HTTP_PORT=8080
export HTTP_HOST=0.0.0.0
export ENDPOINT_PATH=/mcp

Required and Optional Environment Variables

The following table lists all configuration options recognized by the server:

Variable	CLI Equivalent	Required	Default	Description
API_BASE_URL	--api-base-url / -u	Yes	—	Base URL of the target REST API
OPENAPI_SPEC_PATH	--openapi-spec / -s	Yes	—	Path or URL to the OpenAPI specification
TRANSPORT_TYPE	--transport / -t	No	stdio	Transport protocol (stdio or http)
HTTP_PORT	--port / -p	No	3000	HTTP server port
HTTP_HOST	--host	No	127.0.0.1	HTTP server host
ENDPOINT_PATH	--path	No	/mcp	HTTP endpoint path
API_HEADERS	--headers / -H	No	—	Comma-separated key:value headers for API requests
SERVER_NAME	—	No	mcp-openapi-server	Server identifier
SERVER_VERSION	—	No	1.0.0	Server version
TOOLS_MODE	—	No	all	Tool loading mode (all or dynamic)
DISABLE_ABBREVIATION	—	No	—	Set to true to disable name optimization

Practical Configuration Examples

Running with a Custom Port via CLI

To start the server on port 8085 accessible from any network interface:

npx ts-node ./mcp-openapi-server/src/index.ts \
  --transport http \
  --port 8085 \
  --host 0.0.0.0 \
  --path /my-mcp \
  --api-base-url https://api.example.com \
  --openapi-spec ./spec.yaml

The server will listen at http://0.0.0.0:8085/my-mcp.

Using a .env File for Production

Create a .env file in the repository root:

TRANSPORT_TYPE=http
HTTP_PORT=8080
HTTP_HOST=0.0.0.0
ENDPOINT_PATH=/mcp
API_BASE_URL=https://api.example.com
OPENAPI_SPEC_PATH=./openapi.json
API_HEADERS=Authorization:Bearer abc123,X-API-Key:mykey

Then start the server:

npm run start:mcp

The loadConfig() function automatically reads these values when the environment variables are present in the shell environment.

Mixing CLI Arguments and Environment Variables

CLI arguments override environment variables. In this example, the port comes from the flag while the host comes from the environment:

export HTTP_HOST=0.0.0.0
export API_BASE_URL=https://staging.api.com

npx ts-node ./mcp-openapi-server/src/index.ts \
  --transport http \
  --port 9000

The server binds to 0.0.0.0:9000 and uses the staging API base URL.

Summary

• The MCP OpenAPI Server in castrozan/tcc uses a hierarchical configuration system where CLI arguments take precedence over environment variables.
• The loadConfig() function in mcp-openapi-server/src/config.ts handles all parsing logic, defaulting to port 3000, host 127.0.0.1, and path /mcp for HTTP transport.
• Required variables include API_BASE_URL and OPENAPI_SPEC_PATH (or their CLI equivalents --api-base-url and --openapi-spec).
• You can configure the server port and environment variables using .env files, shell exports, or command-line flags depending on your deployment needs.

Frequently Asked Questions

What is the default server port?

The default server port is 3000 when using HTTP transport. This is defined in mcp-openapi-server/src/config.ts where the httpPort variable falls back to 3000 if neither the --port CLI argument nor the HTTP_PORT environment variable is set.

Do CLI arguments override environment variables?

Yes. The configuration system in castrozan/tcc follows a strict precedence order: CLI arguments take priority over environment variables, which in turn take priority over default values. For example, passing --port 8080 overrides the HTTP_PORT environment variable.

How do I configure the server to listen on all network interfaces?

Set the host to 0.0.0.0 using either the --host CLI flag or the HTTP_HOST environment variable. The default host is 127.0.0.1 (localhost only), so you must explicitly change it to accept external connections.

What happens if required environment variables are missing?

The loadConfig() function in mcp-openapi-server/src/config.ts throws an informative error during startup if required values like API_BASE_URL or OPENAPI_SPEC_PATH are missing. The server will not start until these are provided via CLI arguments or environment variables.

{
  "mcpServers": {
    "instagit": {
      "command": "npx",
      "args": ["-y", "instagit@latest"]
    }
  }
}