Tool annotations provide hints about a tool’s nature and side effects, without affecting the model’s context or being relied upon for security decisions

VS Code landed support in Insiders:

• title: A human-readable name for the tool, used by clients to label UI elements
• readOnlyHint: Set to true if the tool truly has no side effects, enabling clients to prevent unintended state changes. VS Code will provide an option to auto-approve read-only tools, similar to how it treats low-risk, read-only internal tools.