What is Tool Use? (Function Calling)

Tool use lets AI access external tools, APIs, and databases to complete tasks. Learn how function calling works and why it matters for brand visibility.

The capability of AI systems to call external tools, APIs, and services to gather information or complete tasks beyond their training data.

Tool use transforms AI from a static knowledge system into an active assistant that can browse the web, run code, query databases, make API calls, and interact with external services. When ChatGPT uses Bing to look up current stock prices or Claude writes and executes Python code, that's tool use in action. It's the bridge between what an AI knows and what it can do.

Deep Dive

Tool use represents one of the most significant architectural shifts in modern AI. Rather than relying solely on training data that becomes stale the moment training ends, AI systems can now reach out to the real world for current information and capabilities. The mechanism is straightforward: the AI recognizes when a user's request requires external capabilities, formulates a structured call to the appropriate tool, interprets the results, and incorporates them into its response. OpenAI calls this "function calling" and released it in June 2023. Anthropic, Google, and others followed with similar implementations. The technical process involves the model outputting a structured JSON object specifying which tool to call and with what parameters. The practical applications are extensive. ChatGPT's Code Interpreter can execute Python to analyze data, create visualizations, or process files. Perplexity's web search tool queries the internet in real-time, returning cited results within 2-3 seconds. Enterprise implementations connect AI to internal databases, CRM systems, scheduling tools, and custom APIs. Microsoft's Copilot integrates tools across the entire Office suite. For marketers, tool use has significant implications. When an AI browses the web to answer a query about your industry, it's selecting which sources to trust and cite. The AI becomes a gatekeeper, deciding which information deserves inclusion. A product comparison powered by real-time search will pull from specific review sites, competitor pages, and pricing databases - making your presence on those sources newly critical. The reliability varies by implementation. Some tools are tightly controlled: Code Interpreter runs in a sandboxed environment. Others are more unpredictable: web browsing tools might return outdated cache results or misinterpret page content. Enterprise deployments typically include guardrails and approval workflows for sensitive operations. Tool use also enables AI agents - systems that chain multiple tool calls together to accomplish complex tasks. An AI might search the web, synthesize findings, write code to analyze the data, and generate a report, all from a single prompt. This agentic capability is where tool use becomes particularly powerful, and where brand visibility in tool-accessible sources becomes even more important.

Why It Matters

Tool use fundamentally changes how AI gathers and synthesizes information about your brand. When a customer asks an AI assistant for product recommendations, that AI might browse your website, check review platforms, query pricing databases, and pull from news sources - all in seconds. This creates a new visibility imperative: being present and accurate in tool-accessible sources. Traditional SEO optimized for human search. Now you also need to consider how your information appears when AI tools query it programmatically. The AI selecting which sources to include becomes a critical intermediary between your brand and potential customers.

Key Takeaways

Tools extend AI beyond static training data: Without tools, AI knowledge is frozen at training time. Tool use enables real-time information access, code execution, and integration with live systems and databases.

Function calling is the standard mechanism: AI outputs structured JSON specifying which tool to call and with what parameters. This standardized approach, pioneered by OpenAI in 2023, is now universal across major providers.

Web browsing tools select sources on your behalf: When AI searches the web, it chooses which sources to trust and cite. Your brand's presence in tool-accessible sources directly affects whether you appear in AI responses.

Agents chain tools for complex tasks: Advanced AI systems combine multiple tool calls sequentially: searching, analyzing, writing, and executing. This amplifies both the capability and the importance of being in retrievable sources.