Agents & tool use Protocols

Function calling, now also called tool calling, lets an application describe external functions to a model, which then decides whether to emit JSON arguments for one of them — the route by which models reach data and actions outside their training data.

The Model Context Protocol (MCP) is an open standard for connecting AI assistants to the systems where data lives. Anthropic open-sourced it on 25 November 2024 and later donated it to the Agentic AI Foundation.

Google's 2025 open protocol for discovery, communication, and collaboration across agents from different vendors or frameworks.

An open protocol announced by Google on 17 September 2025 for securely initiating and settling payments carried out by AI agents across platforms, using signed Mandates as verifiable proof of a user's instructions.

An open standard released by OpenAI with Stripe in September 2025 that lets AI agents, people and businesses complete purchases together, and the basis of Instant Checkout in ChatGPT.

Agent Skills are folders of instructions, scripts and resources that Claude loads when they are relevant to a task. Anthropic introduced them on 16 October 2025 and donated the open standard to the Agentic AI Foundation in October 2026.

AG-UI is an open, event-based protocol that connects AI agents to user-facing applications, standardising how agent state, UI intents and user interactions flow between an agent backend and a front end.

ACP (Agent Communication Protocol) is an open protocol for agent interoperability, connecting AI agents, applications and humans through a standardised RESTful API. It was developed under the Linux Foundation alongside BeeAI and now sits within A2A, with a migration guide for existing users.

NLWeb is a set of open protocols and open-source tools that give websites a conversational interface, returning Schema.org JSON over natural language and doubling as an MCP server so the same API serves people and AI agents.