Simon Willison’s Weblog

Anthropic Trust Center: Brave Search added as a subprocessor (via) Yesterday I was trying to figure out if Anthropic has rolled their own search index for Claude's new web search feature or if they were working with a partner. Here's confirmation that they are using Brave Search:

Anthropic's subprocessor list. As of March 19, 2025, we have made the following changes:

Subprocessors added:

• Brave Search (more info)

That "more info" links to the help page for their new web search feature.

I confirmed this myself by prompting Claude to "Search for pelican facts" - it ran a search for "Interesting pelican facts" and the ten results it showed as citations were an exact match for that search on Brave.

And further evidence: if you poke at it a bit Claude will reveal the definition of its web_search function which looks like this - note the BraveSearchParams property:

{
  "description": "Search the web",
  "name": "web_search",
  "parameters": {
    "additionalProperties": false,
    "properties": {
      "query": {
        "description": "Search query",
        "title": "Query",
        "type": "string"
      }
    },
    "required": [
      "query"
    ],
    "title": "BraveSearchParams",
    "type": "object"
  }
}

# 3:07 pm / anthropic, claude, generative-ai, llm-tool-use, search, ai, llms

The “think” tool: Enabling Claude to stop and think in complex tool use situations (via) Fascinating new prompt engineering trick from Anthropic. They use their standard tool calling mechanism to define a tool called "think" that looks something like this:

{
  "name": "think",
  "description": "Use the tool to think about something. It will not obtain new information or change the database, but just append the thought to the log. Use it when complex reasoning or some cache memory is needed.",
  "input_schema": {
    "type": "object",
    "properties": {
      "thought": {
        "type": "string",
        "description": "A thought to think about."
      }
    },
    "required": ["thought"]
  }
}

This tool does nothing at all.

LLM tools (like web_search) usually involve some kind of implementation - the model requests a tool execution, then an external harness goes away and executes the specified tool and feeds the result back into the conversation.

The "think" tool is a no-op - there is no implementation, it just allows the model to use its existing training in terms of when-to-use-a-tool to stop and dump some additional thoughts into the context.

This works completely independently of the new "thinking" mechanism introduced in Claude 3.7 Sonnet.

Anthropic's benchmarks show impressive improvements from enabling this tool. I fully anticipate that models from other providers would benefit from the same trick.

# 7:17 pm / prompt-engineering, anthropic, claude, generative-ai, ai, llms, llm-tool-use