MCP server configuration and transport protocols

Transport protocols

You can set one of the following transport protocols when starting the MCP server so that it operates correctly for your environment.

Transport	Best for	How it works	Usage
`stdio`	Local development and direct integration with MCP clients	Uses standard input/output for JSON-RPC message communication	Automatically used when no specific transport mode is configured
`streamable-http`	Distributed setups, internal environments	HTTP-based transport with support for both direct HTTP requests	Enable by setting `TRANSPORT_MODE=streamable-http`

HTTP mode configuration

You can only use the MCP server locally. If you use the StreamableHTTP transport protocol in production, always configure the MCP_ALLOWED_ORIGINS environment variable to restrict access to trusted origins only.

Limiting access to trusted origins helps prevent DNS rebinding attacks and other cross-origin vulnerabilities.

In HTTP mode, you have multiple options to provide your Vault configuration. The MCP server considers the following options, in order:

HTTP Query: VAULT_ADDR
HTTP Headers: VAULT_ADDR, X-Vault-Token, and X-Vault-Namespace
Environment Variables: Standard VAULT_ADDR, VAULT_TOKEN, and VAULT_NAMESPACE env vars

Environment variables

Use the following environment variables to configure MCP server behavior.

MCP_ALLOWED_ORIGINS (string : "")

Comma-separated list of allowed URLs for Cross-Origin Resource Sharing (CORS).

Example: export MCP_ALLOWED_ORIGINS="http://mcp.client.com:5000,http://localhost"

MCP_CORS_MODE (string : "strict")

Configures how the MCP server handles cross-origin HTTP requests.

Key	Description
`strict`	Requests must be same-origin. The MCP server rejects any cross-origin requests with an error message
`development`	Allow secure cross-origin data access if the server replies with an appropriate origin header
`disabled`	Disables CORS checks for cross-origin requests

Example: export MCP_CORS_MODE="development"

MCP_ENDPOINT (string : "/mcp")

HTTP server endpoint path for the MCP server.

Example: export MCP_ENDPOINT="/api/mcp"

MCP_RATE_LIMIT_GLOBAL (string : "10:20")

The global maximum steady-state (rps) and spike (burst) requests rates for the MCP server in rps:burst format.

Example: export MCP_RATE_LIMIT_GLOBAL="100:200"

MCP_RATE_LIMIT_SESSION (string : "5:10")

The per-session, steady-state (rps) and spike (burst) MCP request rate in rps:burst format. Session limits cannot exceed the global server limits.

Example: export MCP_RATE_LIMIT_SESSION="20:40"

MCP_TLS_CERT_FILE (string : "")

Path to a PEM-encoded TLS certificate file on the local disk. Used for TLS communication with the server. The specified certificate must match to the private key set with MCP_TLS_KEY_FILE.

Example: export MCP_TLS_CERT_FILE="/path/to/certs/mycert.pem"

MCP_TLS_KEY_FILE (string : "")

Path to a PEM-encoded, TLS private key file. The specified key must match to the certificate set with MCP_TLS_CERT_FILE.

Example: export MCP_TLS_KEY_FILE="/path/to/keys/myprivatekey.pem"

VAULT_NAMESPACE (string : <unset>)

Root namespace for the MCP server command. Setting a default namespace allow relative mount paths.

Example: export VAULT_NAMESPACE="admin"

VAULT_TOKEN (string : <required>)

A Vault-issued authentication token that authenticates the AI client to Vault. See the tokens concepts page for more information on token types.

Example: export VAULT_TOKEN="hvs.xxxxxxxxxxxxxxxxxxxxxxxx"

TRANSPORT_HOST (string : "127.0.0.1")

Host IP address the MCP server should bind to for HTTP mode.

Example: export TRANSPORT_HOST="0.0.0.0"

TRANSPORT_MODE (string : "")

Default transport mode for the MCP server.

Key	Description
`http`	enables HTTP mode

Example: export TRANSPORT_MODE="http"

TRANSPORT_PORT (string : "8080")

Port number used with HTTP mode.

Example: export TRANSPORT_PORT="3000"

VAULT_ADDR (string : 'https://127.0.0.1:8200')

Address of the Vault server.

Example: export VAULT_ADDR="https://mydomain/vault:8200"