MCP transports & config

Lime supports six MCP transports. The right choice depends on whether the server runs as a local process, a remote HTTP service, or an in-process plugin.

Transport overview

Transport	Best for	Wire shape
stdio	Local processes (npm packages, Python scripts, binaries).	NDJSON over stdio. Not LSP-style Content-Length framing.
sse	Remote services with one-way streams.	JSON-RPC over Server-Sent Events.
http	Remote services that prefer plain HTTP.	JSON-RPC over HTTP POST with optional polling.
ws	Remote services with bidirectional streams.	JSON-RPC over WebSocket.
sdk	In-process Lime SDK servers (Rust binaries linking the SDK).	In-memory channels.
lime-proxy	Bridging a foreign transport via a Lime-managed shim.	Lime spawns a proxy that handles its own transport details.

The type value is also accepted as streamable-http (alias for http).

Stdio framing is NDJSON

A persistent footgun: real-world MCP servers use newline-delimited JSON over stdio. They do not use LSP-style Content-Length headers. Implementations that get this backwards hang silently.

Configuration

MCP servers live under mcpServers in any settings file:

{
  "mcpServers": {
    "sqlite": {
      "type": "stdio",
      "command": "npx",
      "args": ["-y", "@modelcontextprotocol/server-sqlite", "--db-path", "./data.db"],
      "env": { "API_KEY": "..." },
      "toolCallTimeoutMs": 30000
    },
    "remote-api": {
      "type": "sse",
      "url": "https://api.example.com/mcp",
      "headers": { "Authorization": "Bearer ${TOKEN}" }
    },
    "ws-server": {
      "type": "ws",
      "url": "wss://tools.example.com/mcp"
    }
  }
}

Variables in the form ${NAME} are expanded from the environment when the server starts.

stdio fields

Field	Type	Default	Notes
type	"stdio"	—	Required.
command	string	—	Executable. Resolved on PATH.
args	string[]	[]	Arguments.
env	object	{}	Extra env vars (merged on top of the parent process env).
cwd	string	repo	Working directory.
toolCallTimeoutMs	number	30000	Per-call timeout.

Remote (sse / http / ws) fields

Field	Type	Notes
type	enum	"sse", "http", or "ws".
url	string	Full URL (for ws, the scheme is ws:// or wss://).
headers	object	Per-request HTTP headers. Trust-gated — see the warning below.
oauth	object	OAuth client config. See OAuth section.

Headers are trust-gated

The headers field is honored only when the server’s enclosing scope is trusted (User / Local). A project-scope server with headers defined is loaded with the headers stripped and a diagnostic warning logged.

OAuth

For remote servers that require OAuth:

{
  "type": "http",
  "url": "https://api.example.com/mcp",
  "oauth": {
    "issuer": "https://auth.example.com",
    "clientId": "lime-client",
    "scopes": ["mcp:tools", "mcp:resources"]
  }
}

Lime stores tokens encrypted under ~/.lime/. Refresh is automatic. The first time the server is reached, the user is prompted to complete the auth flow in a browser.

Per-tool allow / deny on a server

{
  "mcpServers": {
    "sqlite": {
      "type": "stdio",
      "command": "npx",
      "args": ["-y", "@modelcontextprotocol/server-sqlite"],
      "tools": {
        "allow": ["sqlite/query"],
        "deny":  ["sqlite/exec"]
      }
    }
  }
}

Tool-level allow/deny is evaluated before the global per-tool policy.

Auto-approval

A server can declare tool annotations that mark calls as safe to run without a prompt:

{
  "tools": {
    "autoApprove": ["sqlite/query"]
  }
}

Hooks can also auto-approve based on input shape via PreToolUse. See Hooks.

Telemetry & redaction

• All MCP tool inputs and outputs are redacted in event logs by default. Output capping: LIME_MAX_MCP_OUTPUT_TOKENS (default 2000).
• Connect timeouts: LIME_MCP_CONNECT_TIMEOUT_MS (default 10000).
• Concurrency caps for the eager-startup connect wave: LIME_MCP_CONNECTION_BATCH_SIZE and LIME_MCP_REMOTE_CONNECTION_BATCH_SIZE.

Manage servers from the CLI

# Stdio (default transport)
lime mcp add sqlite npx -y @modelcontextprotocol/server-sqlite \
            --db-path ./data.db

# Remote — sse | http
lime mcp add --transport sse --scope user remote https://example.com/sse

# Drop in a full JSON config for one server (any transport, including ws / sdk / lime-proxy)
lime mcp add-json my-server '{"type":"http","url":"https://example.com/mcp"}' --scope project

# Inspect + manage
lime mcp list
lime mcp get sqlite
lime mcp enable sqlite
lime mcp disable sqlite
lime mcp remove sqlite --scope user
lime mcp reset-project-choices

lime mcp add only emits stdio, sse, and http entries. For the other transports (ws, sdk, streamable-http, lime-proxy) use lime mcp add-json or edit your settings file directly.

…or inside the REPL:

/mcp list
/mcp status
/mcp browse           # interactive registry picker
/mcp enable sqlite
/mcp reconnect sqlite