You enable advanced tool use with Claude Opus 4.5 by defining tools inside your API request and connecting those tools to the new expanded tool-use features in the Claude Developer Platform. At the API level, you add a tools array to your Messages API call, defining each tool with a name, JSON schema, and description. Once this is in place, Claude Opus 4.5 can choose when to call a tool, return a tool_call in its output, and wait for you to execute the function and send the result back as another message. Opus 4.5 supports both user-defined client tools and Anthropic-defined tools such as the browser, code editor, and computer-use APIs.
To make tool use “advanced,” you can incorporate features like tool search, input examples, and programmatic overrides. Tool search lets Claude dynamically identify the right tool based on semantic descriptions, which is useful when your system has dozens of tools. Input examples help clarify how a tool should be used, reducing malformed arguments and making tool calls more reliable. Programmatic tool steering lets your orchestrator inject constraints or override tool selection to match business rules, while still allowing Claude to plan and reason around tools. These capabilities are all surfaced through Anthropic’s API, SDKs, and proxy layers like LiteLLM.
In real engineering workflows, tool use becomes most powerful when combined with retrieval. You might define a retrieval tool backed by a vector database such as Milvus or Zilliz Cloud, allowing Claude Opus 4.5 to request relevant documents or code snippets on demand. This keeps prompts light while still supplying the model with the information it needs. Complex systems often have tools for reading files, writing patches, running tests, invoking APIs, or updating tickets. Claude Opus 4.5’s tool planning improves reliability here, but safety comes from your implementation: validate tool inputs, log all calls, and keep powerful tools gated by role checks or business logic.