When an endpoint or syntax is already used as a contract (e.g., chart grammar shared across features, or a stateful editor URL), avoid creating parallel interfaces or polluting the contract with unrelated concerns. Apply this as: - Prefer extending an existing syntax/API instead of adding a separate, parallel one (reduces duplication and client/parser divergence). - If a URL encodes application state, keep the URL’s state-related parameters clean; don’t add marketing/tracking query params to the same URL the app uses to store/load state. Example (clean stateful editor URL): ```ts // Bad: pollutes a stateful URL used by the editor const liveUrl = 'https://mermaid.live/edit?utm_source=mermaid_js&utm_medium=editor_selection&utm_campaign=open_source'; // Good: keep only the contract URL; send analytics separately const liveUrl = 'https://mermaid.live/edit'; ```