MCP tool
An MCP tool is a single named action that an MCP server offers, complete with a description and a schema for its inputs. When Claude Code decides a tool is relevant, it calls it with specific arguments and gets a result back, the same way it would call any other function.
Why it matters
A server can expose several tools. Claude Keychain's server exposes list_secret_names, which returns names only, and run_with_secrets, which runs a command you specify with a named secret injected as an environment variable and returns just the command's output.
Can Claude call a tool without asking me?
Claude Code normally asks for permission before running a tool that can change something or access data, and you can configure how strict that is.
Can a tool see previous tool calls?
No. Each call gets only the arguments it is given and returns only its own result.
Related
Looking for a different way to manage your keys? See the best Claude Code API key manager alternatives, or browse every term in the glossary.