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LLM API Tool Comparison - OpenAI vs Claude vs Grok vs Gemini

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LLM platforms offer API-level tools to extend model capabilities beyond basic text completion. These tools let models call functions, execute code, retrieve information, and handle files in a structured way instead of only replying in natural language. The sections below compare the official, documented tools and structured capabilities provided by OpenAI’s ChatGPT API, Anthropic’s Claude API, Elon Musk’s xAI Grok API, and Google’s Gemini API. Key features like function calling, code execution, file or data retrieval, and other structured tool use are described for each vendor, followed by a high-level comparison to the emerging Model Context Protocol (MCP) standard.

Example function-calling workflow (from Google Gemini docs). The LLM can return a function name & arguments instead of a final answer, prompting the application to execute that function and return results. The model then uses those results to produce a completion. function-calling-flow

OpenAI (ChatGPT) – API Tools and Capabilities

OpenAI’s API (notably the Chat Completions API for GPT-3.5 and GPT-4 models) introduced function calling in mid-2023, allowing developers to define custom functions that the model can call with JSON-formatted arguments. This mechanism lets ChatGPT produce structured outputs (function calls) instead of plain text, enabling integration with external tools and APIs. In late 2024 and early 2025, OpenAI expanded its official toolset as part of an “Agents” platform, adding built-in tools for web browsing, file retrieval, and code execution. Below are OpenAI’s key API-level tool features:

Function Calling (Custom Functions)

  • Description: OpenAI’s function calling feature allows GPT models to call developer-defined functions by name with arguments in JSON. The developer provides a list of function definitions (name, description, and expected parameters using JSON Schema) in the API request. The model can choose to output a JSON object with a target function name and arguments instead of a normal message. This structured output indicates the model wants the application to execute that function. The function calling flow involves the model deciding if a function is needed, returning a JSON payload, the developer’s code executing the function, and then the model using the function result to form its final answer (see diagram above).

  • API Structure: In OpenAI’s Chat Completions API, function calling is enabled by including a "functions" array in the request, each with a name, description, and parameters schema (following JSON Schema). The model’s response may contain a function_call field with the chosen function name and a JSON string of arguments. Developers can also guide the model by specifying function_call: "auto" (allow model to decide) or "none"/"function_name" to control whether and which function to call. OpenAI’s API now supports strict JSON mode – setting strict: true in the function definition – which guarantees the model’s generated arguments exactly match the provided schema (preventing hallucinated or malformed inputs).

  • Notable Details: OpenAI’s function calling is flexible – models can call multiple functions in sequence if needed. Recent model versions even support parallel function calls (the model can return an array of function calls to execute concurrently). This is useful for cases like fetching data from two sources at once (e.g. weather in two cities). Function calling is available on GPT-3.5 Turbo and GPT-4 models (and newer developer-focused GPT-4.1 models) via the Chat Completions API.

  • Primary Use Cases: Enabling ChatGPT to fetch external data, perform calculations, or take actions on behalf of the user. For example, an assistant can call a get_weather(city) function to retrieve live weather info, query a database for account data when asked about “my recent orders,” perform math via a calculator function, or schedule an event via a calendar API. OpenAI notes that function calling allows “connecting LLMs to external tools and systems,” empowering assistants to do things like look up knowledge, execute commands, or integrate with software.

Built-in Tools (OpenAI Agents SDK)

  • Web Search: OpenAI’s Agents platform provides an official Web Search tool (similar to ChatGPT’s browsing capability) that the model can use to search the internet for up-to-date information. When enabled, the model can formulate search queries and retrieve results which it uses to answer user questions with current data. (This was previously available only via ChatGPT plugins or the browsing beta; now it’s an OpenAI-provided tool in the API.) Use cases: Answering questions about latest news, factual queries beyond the model’s training cutoff, or any task requiring real-time information.

  • File Search: Another new OpenAI tool is File Search, which allows the model to search and retrieve content from a collection of files or documents. Developers can likely index their data or provide a document repository that this tool queries (for example, searching a knowledge base or personal files for relevant text). Use cases: Retrieval-Augmented Generation scenarios – e.g. finding a policy document to answer a question, retrieving a user’s notes or past emails to incorporate into the response.

  • Computer Use (Code Execution): OpenAI has also introduced a Computer Use tool (analogous to the “Code Interpreter” / Advanced Data Analysis from ChatGPT). This tool lets the model run code or use a sandboxed computing environment to solve problems – for example, running Python to do data analysis, calculations, or file processing. Unlike basic function calling (where the developer’s code executes predetermined functions), the Computer Use tool likely provides a general code execution sandbox on OpenAI’s side or via the SDK. Use cases: Data analysis, converting file formats, performing complex calculations, or debugging code within a conversation.

  • API Usage: These built-in tools are integrated into OpenAI’s API through the Agents SDK and the “Tools” interface. Developers declare which tools are available (e.g. enabling web_search or others), and the model can invoke them as needed. OpenAI’s help docs (as of March 2025) explicitly list Web Search, File Search, and Computer Use as available tools in the API. The model’s decision to use a tool is surfaced in the API response (with a special message or flag), and the Agents SDK helps handle executing the tool and returning results. This design is very similar to Anthropic’s approach (described below), showing a convergence in how tools are handled across vendors.

  • Primary Use Cases: Built-in tools further extend what developers can do with ChatGPT via API. For example, Web Search lets a customer support bot get the latest shipping rates from the web, File Search lets an enterprise chatbot pull answers from internal documents, and Computer Use lets a data assistant run analysis code on provided datasets. These tools help overcome model limitations (stale training data, lack of computational ability, limited knowledge) by bridging to external resources.

Anthropic (Claude) – API Tools and Capabilities

Anthropic’s Claude API supports tool use (function calling) similar to OpenAI, with a robust framework for integrating both developer-defined functions and Anthropic-provided tools. Claude can decide to invoke a tool during a conversation to perform tasks like looking up information, executing code, or editing text. The implementation is split between client-side tools (which the developer implements and runs) and server-side tools (executed on Anthropic’s servers). Key tools/capabilities in Claude’s API include:

Tool Use / Function Calling

  • Description: Anthropic refers to function calling generally as “tool use.” Developers supply a list of available tools in the API request (each with a name, description, and input schema) and a user prompt. Claude’s model then decides if a tool is needed to fulfill the request. If so, Claude’s response will indicate a tool invocation rather than a final answer. Specifically, the API will return a message with stop_reason: "tool_use" when Claude wants to call a tool. The response includes the tool name and a JSON block of arguments that Claude has formulated for that tool call.

  • API Structure: Tools are provided via the Claude Messages API by including a tools list in the request. Each tool has a unique name, a description, and a JSON schema for its input (very much like OpenAI’s function definitions). When Claude decides to use a client-side tool, the API response type is a Tool Use Request (instead of a normal completion) – the developer receives the tool name and args, executes the tool, and then sends a new message with the tool’s result for Claude to incorporate. For server-side tools, the execution is internal: Claude runs the tool on Anthropic’s side and directly incorporates the result into its next message without a round-trip to the developer.

  • Differences from OpenAI: Claude’s tool use is conceptually similar to OpenAI’s function calling but has some different terminology and workflow details. Anthropic distinguishes client tools vs. server tools. For client tools, the developer must handle execution and provide results back (like OpenAI’s approach). For server tools (e.g. a built-in web search), Claude handles execution and the developer simply gets the final augmented answer. Another difference: Anthropic uses a special message format with a tool_result block when returning results to Claude. Overall, the pattern of define → model calls → execute → return result is the same as OpenAI’s.

  • Primary Use Cases: Similar to other LLMs, Claude’s function/tool calling is used to extend its knowledge, perform actions, or do calculations beyond its trained capabilities. For example, Claude could call a get_stock_price(symbol) tool to retrieve real-time stock data, or a send_email(to, content) tool to actually perform an action on behalf of a user. Anthropic specifically notes that tool use lets Claude “perform a wider variety of tasks” by interacting with external functions – whether that means searching for information, using a calculator, accessing a database, or controlling another app.

“Computer Use” (Code Execution Tool – Beta)

  • Description: Computer Use is an Anthropic-provided client-side tool (in beta) that essentially allows Claude to execute code or use a computer environment via the developer’s system. When enabled, Claude can output a request to run some code (for instance, a Python script) as a tool call. The developer’s application would detect the computer_use tool request and execute the code in a sandbox or local environment, then return the output back to Claude as a tool result. This is analogous to giving Claude a “code interpreter” ability, but the execution happens on the client side (Anthropic provides the interface, the developer provides the actual runtime).

  • Example Usage: A user asks Claude to analyze a dataset or perform a complex math operation. Claude decides this would be easier with code, so it issues a computer_use tool request with the code to run. The developer’s system runs the code (e.g. a Python snippet) and captures the result or error, then sends it back to Claude in a formatted tool_result message. Claude then continues the conversation, incorporating the computation results. Anthropic’s documentation suggests Claude 3 is quite capable of writing code for such tool use on the fly, enabling powerful data analysis or coding assistance scenarios.

  • Primary Use Cases: Data science assistance (Claude can write and run code to answer questions about data), mathematical problem solving, format conversion (write a script to convert JSON to CSV, for example), or debugging and testing code. Essentially, Computer Use gives Claude a way to perform any computation it can formulate, expanding its usefulness for coding and analytical tasks.

Text Editor Tool

  • Description: The Text Editor tool (introduced in early 2025) allows Claude to view and modify text files via a set of file-editing commands. This is an Anthropic-defined client tool: developers must implement the file operations on their side (reading/writing files), but Claude is aware of the tool’s capabilities and can request actions like opening a file or replacing text. The tool defines commands such as view (to retrieve file contents or a snippet), insert (to add text at a certain line), str_replace (to replace a string in the file), create (make a new file), and undo_edit (revert the last change).

  • How it Works: The developer advertises the Text Editor tool with the above commands and their input schema (e.g. {"file_path": "...", "line_start": ..., "content": "..."}, etc.). If a user asks Claude to modify some code or edit a document, Claude can issue a tool use request like: text_editor with arguments { "command": "view", "file_path": "script.py", "start_line": 1, "end_line": 100 }. The client then reads those lines from script.py and returns them in a tool_result. Claude may then propose changes by calling text_editor again with command: "str_replace" and appropriate args to alter the file. Through successive tool calls, Claude can iteratively edit the file.

  • Primary Use Cases: This tool is geared toward code editing and content modification tasks. For instance, a developer can have Claude act as a pair programmer: Claude can fetch the content of a source code file, suggest and apply edits (fixing bugs or refactoring) by actually modifying the file via the tool, and even create new files as needed. It could also be used for document editing (e.g. find-and-replace in a text or markdown file). Essentially, the Text Editor tool lets Claude be an “agentic” editor, not just suggesting changes in text but actually carrying them out in a controlled way.

Web Search Tool (Server-Side)

  • Description: Anthropic provides a built-in Web Search tool that Claude can use to fetch information from the internet. This is a server-side tool – the execution happens on Anthropic’s servers, so the developer doesn’t need to implement the actual web search logic. When enabled in the API request, Claude can decide to call the web_search tool with a query, and the Anthropic backend will perform the search (likely using an integrated search API) and return the results directly to Claude. Claude then incorporates those results into its answer.

  • Usage: The developer must include the web_search tool (with a specific version identifier, e.g. web_search_20250305) in the request to allow Claude to use it. If the user asks something like “What’s the latest news about AI?”, Claude may call web_search internally. The model’s response to the developer won’t explicitly show the search query and results step; instead, Claude will produce a final answer that already includes information gleaned from the web. Essentially, the tool use and result integration happen in one shot on Anthropic’s side. (However, if one were logging Claude’s reasoning, one might see that it used the tool under the hood.)

  • Primary Use Cases: Any query that requires up-to-date or factual information beyond Claude’s training data can benefit from web search. This includes news queries, questions about recent events or figures, real-time data (like current stock prices, sports scores), etc. It improves the relevance and accuracy of Claude’s responses for time-sensitive or factual questions by giving it access to current data. Developers can thus build assistants that combine Claude’s language skills with live information retrieval.

Other Notable Features

  • Extended Context and PDF Support: (While not exactly “tools,” it’s worth noting.) Claude has features like extended context windows and direct PDF support. For example, Claude can accept an entire PDF document as input and then answer questions about it or summarize it – effectively doing retrieval/Q&A on that file. This is supported via the Claude API by sending the PDF content (or perhaps a file handle) in a message. It’s another way Claude can handle file content, complementing the more interactive text editor or file search style tools.

  • Token-Efficient Tool Calls: Anthropic has introduced optimizations like Token-Efficient Tool Use (beta) which reduce the prompt overhead of tool definitions. This means developers can enable a mode where tool specifications don’t consume as many tokens in the conversation, making tool-augmented interactions more cost-effective. This is more of an API efficiency improvement than a user-facing tool, but it underscores Anthropic’s focus on refining the tool-use experience.

xAI (Grok) – API Tools and Capabilities

xAI’s Grok model (released in late 2023 by Elon Musk’s AI company) also provides function-calling and tool-use features via its API. Grok’s design borrows from the precedents set by OpenAI and others, with some tweaks in control and possibly integration with real-time information (one of Grok’s selling points was accessing up-to-date data, given its connection to the X platform). The official Grok API documentation mentions support for tools (functions) and even web search capabilities:

Function Calling (Tools) in Grok API

  • Description: Grok allows developers to pass in a list of tools (currently only function tools are supported) that the model can use. Each function tool is described with a name, description, and parameters (just like OpenAI’s JSON schema approach). The model will consider these tools during conversation and can decide to return a JSON-formatted function call when appropriate. This enables Grok to connect to external functions/APIs to fulfill user requests. Essentially, it’s the same paradigm of structured output = function call.

  • API Structure: According to available documentation, the request can include a tools array of function definitions (up to 128 functions). Grok also provides a parameter called tool_choice to control tool usage strategy. This is a notable difference: developers can set tool_choice to "auto" (model decides to call a tool or not, which is the default if tools are provided), "none" (disable tool use – model must answer directly), or "required" (force the model to must call one of the tools). There’s even an option to force a specific function (by name) as the tool to call. This explicit control can help in testing or ensuring certain workflows.

  • Execution Flow: When Grok decides to use a function tool, it outputs the function name and arguments in JSON (similar to other models). The client application then needs to execute the corresponding function and provide the result back to the model for it to continue. The format of responses and subsequent calls aligns with the general function-calling pattern (stop reason or flagged message indicating a tool call). Grok’s API likely uses a field (like tool_calls or a special role) in the response to convey the function call, analogous to OpenAI’s function_call or Anthropic’s stop_reason: tool_use. After executing, the developer would append the function’s result into the conversation (so Grok can use it in a follow-up answer).

  • Primary Use Cases: Similar use cases as OpenAI/Claude – retrieving external data, performing calculations, or taking actions on behalf of the user. For example, Grok could call a get_news(topic) function to fetch latest news headlines, or a calculate(expression) function to do math. xAI has emphasized Grok’s ability to handle real-time information and queries, so function calling would be used to bridge to real-time data sources (e.g. fetching data via an API). Overall, it enables building AI agents that can interact with the world (or a user’s environment) rather than being static.

  • Additional Features: The Grok API supports advanced options like parallel function calls (similar to OpenAI) and structured outputs. Documentation indicates a parallel_tool_calls boolean to enable the model potentially calling multiple functions in parallel. Grok also supports an explicit response formatting mechanism with JSON Schema, beyond function calling. Developers can provide a response_format with a schema to force the model’s answer to conform to a certain JSON structure. This is useful for getting structured data directly as an answer (if not using a function). It’s analogous to OpenAI’s “structured output” mode and shows Grok’s focus on predictable outputs for enterprise use.

Web Search Integration

  • Description: xAI Grok has the ability to perform web searches and incorporate up-to-date information, aligning with Elon Musk’s aim for Grok to be “curious and have broad knowledge.” Official API references suggest a built-in web search tool. In the Grok API, this appears as a parameter web_search_options. By providing web_search_options (e.g. specifying how many results or context), the developer can enable Grok to query the web for information relevant to the user’s prompt.

  • How it Works: When web search is enabled, Grok’s model can decide to perform a search as part of answering a question. The actual search is likely handled by xAI’s backend (perhaps leveraging the Bing API or another search engine, given X’s partnership or data access). The model receives the search results and uses them to formulate a final answer. This is a server-side operation – the developer doesn’t implement the search, just toggles it via the API options. For instance, if asked “What’s the latest on climate policy?”, Grok might internally run a web search and then answer with the information it found.

  • Primary Use Cases: Any query requiring current, factual information that is not in the model’s training data. This includes news, recent facts, live sports or finance data, etc. It helps keep Grok’s responses up-to-date and grounded. Musk has hinted that Grok is tuned to have a bit of wit and up-to-date knowledge (including being aware of X/Twitter content), so web search is central to that capability. In enterprise use, web search (or variations of it) could be used to let the model check internal knowledge bases or the internet as needed.

Other Capabilities

  • Multimodal Inputs: The xAI API documentation indicates Grok supports multiple message types – not just text, but also documents (like .txt or .pdf files), images, and audio in the conversation input. This means developers can provide a PDF or image as a message, and Grok will process it (if the model version supports those modalities). While not a “tool” in the sense of function calling, this is a powerful feature for file handling – e.g. you can directly feed a PDF and ask Grok questions about it (similar to how Claude can handle PDFs). This suggests Grok’s API has built-in file parsing capabilities for certain formats, which is a form of retrieval (the model will read the file content as context).

  • Use in Practice: A developer might send a user message with an attached PDF and ask “Summarize the key points from the attached document.” Grok would ingest the PDF (perhaps via an embedding or internal parser) and then use its content to produce the answer. This bypasses the need to manually copy text or implement a separate retrieval function. It’s officially documented as supported modalities, indicating xAI’s focus on a versatile AI assistant.

In summary, xAI’s Grok aligns with the industry standard of function calling/tool use. It adds fine-grained control (tool_choice flags) and emphasizes real-time knowledge via web search. It also natively handles multimodal inputs. These tools make Grok capable of dynamic and current information access, giving it a competitive feature set alongside OpenAI and Anthropic.

Google (Gemini) – API Tools and Capabilities

Google’s Gemini, the next-generation family of models from Google DeepMind (available via the Google Cloud Vertex AI Generative AI API), also supports structured tool use. Google often refers to this as function calling, and it works analogously to OpenAI’s approach. Gemini’s API was introduced with function calling support from the start (especially in the Gemini 2 models, late 2023), and Google has been aligning with emerging standards to make tool use robust. Key aspects of Google’s tool capabilities:

Function Calling (Tool Use)

  • Description: Function calling in Gemini lets developers connect the model to external tools and APIs. Instead of always answering in free text, Gemini can recognize when a query should be handled by an external function and will return a structured JSON indicating which function to call and with what parameters. Google’s documentation explicitly frames this as allowing the model to “act as a bridge between natural language and real-world actions and data.” Common use cases highlighted include: augmenting knowledge (by fetching from databases/APIs), extending capabilities (using tools for computation, e.g. a calculator or chart generator), and taking actions (interacting with external systems like sending emails or controlling devices).

  • API Structure: In Vertex AI’s API, developers define function “declarations” that include the function name, description, and JSON schema for parameters (similar to OpenAI). They then send the user’s prompt along with these function declarations to the model. The model’s output might be a function call JSON object instead of a final answer. The developer’s code should check the response; if it contains a function call, the developer executes the corresponding function and then sends the function’s result back to the model (usually as a follow-up user message). The model then uses that to produce the final answer. Google provides SDKs and tools (in Python, Node.js, etc.) to streamline this flow.

  • Key Features: Google’s function calling supports JSON Schema definitions for nested and complex parameters, ensuring that models generate well-structured arguments. Their guides emphasize that function calling is also known as “tool use” in general AI parlance. Gemini models that support function calling include the higher-tier versions (e.g. Gemini Pro, Gemini Flash, etc., as noted in Vertex AI documentation). Google has also been rapidly updating these models (e.g., Gemini 2.5, etc.) with improved tool-use capability. The process for function execution is almost identical to OpenAI’s: the model proposes, the developer’s app disposes (executes), then the model finalizes the answer.

  • Primary Use Cases: Google cites examples like getting weather info via an API (augment knowledge), generating a chart from data via a plotting library (extend capability), scheduling a meeting through a calendar API (take action). Essentially, any case where the model alone isn’t enough – either due to lack of current data or inability to perform a task – function calls fill the gap. In enterprise settings on Google Cloud, this could involve integrating Gemini into business workflows: e.g., a chatbot that calls a company’s inventory API to check stock, or an agent that triggers an automation through Google Apps Script via function calls.

Emerging Tool Ecosystem and MCP Integration

  • Open-Standard Approach: Google has shown support for the Model Context Protocol (MCP) – an open standard for tool integration (discussed more below). In fact, code examples in Google’s developer guides demonstrate using MCP to connect Gemini to external tool servers. For instance, Google’s sample shows setting up an MCP stdio server (with a weather service) and connecting Gemini to it, so that when the model needs weather data it communicates through the MCP channel. By adopting MCP, Google allows a standardized two-way connection: the model can call tools (MCP servers) in a uniform way, rather than a Google-proprietary format.

  • Built-in vs Custom Tools: At the time of Gemini’s launch, Google did not heavily advertise proprietary built-in tools (like web search) in the API; instead the focus was on letting developers register the tools they need. However, given MCP and partnerships, one can imagine built-in connectors (for example, a Google Search tool or internal Google services tools) either available or easy to set up. Google’s ecosystem advantage is that many services (Calendar, Gmail, Maps, etc.) could be seamlessly invoked via function calls. In codelabs and tutorials, Google even demonstrates function calling with Google’s own APIs – e.g., a lighting control function or a music player function for a smart home scenario. So, while not “built-in” in the model, Google provides rich examples for integrating their broad API ecosystem with Gemini.

  • Multimodal and Other: Gemini is multimodal; for example, certain Gemini models can accept images as input (Gemini’s predecessors in Vertex AI, like PaLM 2, had a vision model). The API allows specifying modalities like "image" or "audio" in the request. This means you can ask Gemini to analyze an image by providing it directly. Again, this isn’t a “tool call” per se, but a native capability to handle different input types. It complements tool use – e.g., one could imagine a function that processes an image further or a chain where the model describes an image then calls a function based on that description.

  • Primary Use Cases: Beyond those already mentioned, Gemini’s tool usage will shine in enterprise integration – think of a chatbot in Google Cloud that not only answers questions but also runs Google Cloud workflows. For example, an assistant could use function calling to spin up a VM via Google Cloud API, or to fetch data from BigQuery. With MCP and function calls, such actions become possible in a controlled manner. Google’s emphasis on secure and responsible AI means these calls can be audited and permissioned appropriately (e.g., using OAuth for tool authorization). In summary, Gemini’s tools are about turning AI answers into actions, leveraging both custom developer tools and standardized protocols.

Comparison of Tooling Across Vendors

All four vendors – OpenAI, Anthropic, xAI, and Google – have converged on remarkably similar solutions for extending LLMs with tools. Each provides a way to define functions the model can call, uses JSON schemas for structured data exchange, and has some provisions for built-in tool integrations like web search or code execution. The table below highlights key tool capabilities and how they compare:

CapabilityOpenAI (ChatGPT)Anthropic (Claude)xAI (Grok)Google (Gemini)
Function Calling APIYes – developers define functions with JSON schema; model can output function_call with name & args. Supports auto/forced calls and strict JSON mode for valid schemas.Yes – supports “tool use” with client-defined tools (name/description/schema). Model returns stop_reason: tool_use with tool name and JSON args.Yes – supports function tools via a tools list (up to 128). Model returns JSON for function calls. tool_choice parameter allows auto, none, required, or specific tool usage.Yes – supports function calling with JSON schemas for parameters. Model returns structured JSON for a function call if needed. Integrated in Vertex AI SDKs; similar auto decision behavior.
Built-in ToolsWeb Search, File Search, Computer (Code) Execution – introduced via OpenAI’s Agents SDK. These tools are provided by OpenAI (no implementation needed by developer). E.g. web_search fetches internet info, code execution runs Python (formerly ChatGPT plugins) etc.Web Search – built-in server-side tool (Claude executes search and uses results).
Computer Use – anthropic client tool (Claude writes code to run on client’s machine).
Text Editor – anthropic client tool for file viewing/editing. (Anthropic may add more over time.)
Web Search – supported via web_search_options (Grok can pull live web info).
No known proprietary code exec tool announced, but Grok can write code as output (requires user to execute). Emphasis on real-time data and possibly integration with X data.
Not many built-in tools pre-defined by name, but extensive examples of using Google APIs as tools (e.g. Maps, Calendar). Likely to leverage MCP servers for common needs (search, code, etc.). Google may integrate search indirectly (Gemini used in Search/Bard) but for API, developers usually register the needed functions.
Tool Invocation FlowModel outputs function_call -> developer executes function -> model continues with function result. The API returns finish_reason: "function_call" when a function is called. Sequencing of multiple calls supported (including parallel calls in new versions).Model outputs tool request (stop_reason: tool_use) -> developer executes if client tool (or Anthropic auto-executes if server tool) -> model resumes with result. Supports chaining multiple tool uses (Claude can call several tools in series to complete a complex task).Model outputs tool call JSON (likely flagged in response) -> developer executes and returns result -> model continues. Grok allows controlling if a function must be called or not via tool_choice flags. Supports possibly parallel calls (parameter available) and structured output enforcement via schemas.Model outputs function-call JSON in response -> application executes and sends back result -> model produces final answer. Flow is the same pattern. Google’s tools can be chained; with MCP, potentially the model could call multiple steps/tools in a conversation seamlessly.
File HandlingNo direct file upload in chat API (developers must send file content as part of prompt or use File Search tool). File Search tool can retrieve snippets from files provided by developer. Fine-tuning API allows file upload for training, but that’s separate. In ChatGPT UI, had file upload via Code Interpreter.Supports large contexts (100K tokens) so files can be provided as input. Has PDF support – Claude can directly ingest and analyze PDF/Text files. The Text Editor tool allows reading/writing files on the client side. No generic “file search” tool (but developer could implement one, or use MCP integration for data sources).Supports documents in messages – you can input a PDF or text file directly for Grok to read. This covers many file use cases (summarization, Q&A). No explicit separate file search tool, but web search could retrieve online content, and developer functions could handle database/file queries.Google’s focus is on connecting to data sources. With MCP, one can mount enterprise data as an MCP server for the model. Also, Vertex AI offers tools like embedding-based retrieval (via Pinecone/Vertex Matching Engine, outside model). Gemini itself doesn’t ingest files directly via the chat API (as of early versions) except images in certain modes. Instead, one would typically use a function to retrieve file data (e.g., a custom “file_lookup” function hitting a Google Drive API).

As seen above, all vendors share the core idea of LLM as an agent that can call tools. OpenAI and Anthropic have even converged on similar tool names (e.g. “web_search”, “computer use”) and have begun providing out-of-the-box implementations for those. xAI follows closely, with an emphasis on flexibility and real-time info. Google’s approach is deeply integrated into its cloud ecosystem and leans toward open standards and broad developer customizability rather than a fixed set of built-in tools (though official function calling was introduced in Gemini).

MCP and the Future of Tooling (Model Context Protocol)

The Model Context Protocol (MCP) is an emerging open standard that is shaping how these AI tools ecosystems evolve. Introduced by Anthropic in late 2024, MCP provides a standardized way for AI models to connect with external data sources and tools. In essence, MCP formalizes the client–tool interaction: developers run MCP servers that expose certain functionality or data, and AI models (or AI applications) act as MCP clients that can invoke those server capabilities securely. This protocol has significant implications for all the vendors’ tooling:

  • Unified Tool Interface: Prior to MCP, each vendor had its own JSON protocol and conventions for function calling (as detailed above). MCP aims to unify this. For example, instead of writing separate integration code for OpenAI’s function format vs Claude’s tool format vs Google’s, a developer could implement an MCP server for a capability (say, a database lookup or a calculator), and any MCP-compliant model can use it. This cross-vendor compatibility can dramatically reduce integration effort in multi-LLM environments. It moves the ecosystem toward a “write once, use with any model” paradigm for tools.

  • Adoption by Major Vendors: Notably, MCP has quickly gained support. Anthropic open-sourced it, and by March 2025 OpenAI announced official adoption of MCP in its products. Sam Altman (OpenAI’s CEO) confirmed that OpenAI’s new Agents SDK supports MCP, and that ChatGPT (including the ChatGPT desktop app) will incorporate MCP for tool usage. This is a significant development – OpenAI embracing a standard initiated by a competitor – and signals that a neutral protocol is seen as beneficial. Google (DeepMind) is also on board; reports indicate Google’s Vertex AI / Gemini will support MCP or at least is compatible with it. Indeed, Google’s docs show code using an MCP library to connect to a tool. xAI’s stance hasn’t been stated publicly, but given the momentum, it’s likely to follow suit or ensure compatibility.

  • Impact on Tool Ecosystems: If MCP becomes the “universal plumbing” for AI tools, developers can mix and match models with tools much more easily. For example, you might run an MCP server that provides access to your proprietary database. Whether you use Claude or ChatGPT or Gemini, each could call that server through the same protocol, without you rewriting the function spec for each API. This interoperability can lead to richer AI systems – e.g., one could imagine a workflow where different models specialize in different tools but communicate via MCP. It also fosters a marketplace of tools: third parties can offer MCP servers (for weather, stock info, etc.), and any AI model that speaks MCP can use them. In fact, by early 2025 there were already “thousands of integrations” for MCP as per Anthropic, with companies like Replit, Codeium, and Sourcegraph building MCP endpoints for their platforms.

  • Standardization and Interoperability: MCP is likened to a universal open standard for AI connectivity. Much like how HTTP and REST standardized web services, MCP could standardize AI tool usage. This reduces vendor lock-in – if you’ve built an AI agent using OpenAI’s tools and want to switch to Claude, MCP support means your tool layer can remain the same. All major players supporting MCP suggests a future where an “AI agent” isn’t confined to one model’s ecosystem; it can leverage the best of all worlds. It’s also beneficial for safety and security: a standard protocol can include unified ways to handle authentication (indeed MCP is adding OAuth-based auth for tool access) and logging of tool calls, making it easier to monitor and secure AI actions across platforms.

In summary, MCP complements and unifies the vendor-specific tools discussed above. While OpenAI, Anthropic, xAI, and Google each rolled out their own function calling features, MCP is bringing convergence. We’re likely to see the boundaries blur – e.g., OpenAI’s Tools (web search, etc.) might internally use MCP so that they and others call the same backend services. Anthropic’s Claude already leverages MCP for many integrations (Claude can spin up MCP servers to connect to e.g. Slack or GitHub data). Google’s adoption means developers on Vertex AI can readily use the growing MCP tool library. The big picture is that MCP is driving the standardization of AI “agentic” capabilities, ensuring that tool-using AI systems become more compatible, powerful, and easier to develop regardless of the underlying model.