# What Is a Protocol Gateway for AI Agents?

> What a protocol gateway is: the intermediary that translates between MCP, A2A and your APIs, what AWS and Microsoft document and what it means for your store.

URL: https://clione.ai/glossary/protocol-gateway/
Lang: en

A protocol gateway is not a payment gateway, although in a store the two end up close together. It is the piece you put in front of your services so that agents speaking different protocols can use them. The problem it solves is one of numbers: in a few months we have gotten [MCP (Model Context Protocol)](/glossary/mcp/) to connect an agent with its tools, [A2A (Agent2Agent)](/glossary/a2a/) so agents can hand tasks to each other, and [ACP](/glossary/acp/) and [UCP](/glossary/ucp/) for [agentic commerce](/glossary/agentic-commerce/), the purchases an agent makes. No store wants to implement each one separately, and **the gateway promises to speak them all with a single integration**. It is worth knowing what it really does before someone sells you one.

## How it works

We have not found a specification that defines the protocol gateway as a term: neither A2A's nor UCP's mentions it, and the only gateway that appears in UCP is the payment one.[^a2a-spec][^ucp-overview] What exists are products, and their documentation agrees on four functions.

**Translate.** This is the function the piece is named for. AWS's gateway, AgentCore Gateway, **turns requests from agents that use protocols like MCP into API calls and Lambda function calls**, and accepts OpenAPI descriptions, Smithy and Lambda functions as tool sources.[^aws-agentcore-gateway] Azure API Management does the same with the REST APIs it already manages: you choose which API operations are exposed, and each becomes a tool that an MCP client can call. With a written limit: of MCP it only offers tools, not resources or prompt templates.[^azure-apim-mcp]

**Bring together.** An agent does not want ten addresses. agentgateway, an open source project donated to the Linux Foundation in 2025 that joined the [Agentic AI](/glossary/agentic-ai/) Foundation in 2026, offers a single entry point that federates several MCP servers and decides which tools each client sees. It presents itself as a single data plane for HTTP, gRPC, MCP, A2A and language models, so you do not have to maintain a "normal" gateway and an "AI" one.[^agentgateway-faq] AWS describes the same thing in other words: combining APIs, functions, tools, agents and model providers behind a single access point.[^aws-agentcore-gateway]

**Control.** What comes in through the gateway goes through its rules. AgentCore Gateway handles inbound authentication, who the agent is, and outbound authentication, with which credentials it calls each tool.[^aws-agentcore-gateway] In Azure, policies apply to all the tools on a server, such as the documentation's own example that limits calls to five every 30 seconds per IP address.[^azure-apim-mcp] agentgateway adds JWT authentication and role-based access control.[^agentgateway-faq]

**Keep up with versions.** Protocols change fast, and agentgateway lists as one of its features negotiating MCP and A2A version upgrades and falling back when the other side does not support them.[^agentgateway-faq]

## What the protocols say

The protocols themselves explain why translating is not harmless. A2A's documentation admits that an A2A server can expose some of its skills as MCP-compatible resources, and that another agent can discover them that way, perhaps from its [agent card](/glossary/agent-card/). But it specifies that this works best with well-defined skills that can be called like a stateless tool, and that **A2A's strength is stateful collaboration**, which goes beyond a tool call.[^a2a-mcp] A gateway that turns an agent into an MCP tool gains compatibility and loses exactly that: long tasks, intermediate states, the "I need more information".

AWS reflects this in its product: it translates MCP into API calls, but treats A2A traffic as passthrough traffic to the destination agent.[^aws-agentcore-gateway]

UCP solves part of the problem within the standard itself. A merchant declares in its profile, at `/.well-known/ucp`, the same checkout service with several transports: REST, MCP, A2A and one for embedded experiences, each with its own address.[^ucp-overview] The agent picks the one it speaks; nobody has to translate.

## In a store

For a small merchant, the gateway is rarely a piece they install themselves. The translation usually stays with their platform or their payment provider. Stripe, for example, offers Agentic Commerce Suite: **a single integration so that products can be discovered and paid for through several commerce protocols**, with the catalog, [price and availability](/glossary/price-and-availability/) shared with agents, in the United States, Canada and some European countries.[^stripe-acs] In its integrations table, the option to sell through agents (share the catalog, let the agent complete the purchase and receive its payment credentials) uses UCP or ACP.[^stripe-agentic] Stripe does not call it a protocol gateway, but it plays that role: you integrate once and it speaks to each agent in its own language.

When the store does have an API of its own, the gateway decides which part an agent sees. This is how an orders API would look exposed as MCP tools on a gateway of the kind Azure describes, where operations are chosen one by one.[^azure-apim-mcp] It is a **made-up example**: the routes and tool names are invented.

| API operation (made-up example) | MCP tool exposed  | Exposed                  |
| ------------------------------- | ----------------- | ------------------------ |
| `GET /api/products?q=`          | `search_products` | Yes                      |
| `GET /api/products/{id}`        | `get_product`     | Yes                      |
| `GET /api/orders/{id}`          | `order_status`    | Yes, with authentication |
| `POST /api/orders`              | none              | No                       |
| `DELETE /api/products/{id}`     | none              | No                       |


The table shows what a gateway really contributes: it does not only translate, it also **cuts back**. An agent that connects sees three tools, not the whole API, and what it can read or touch is decided in one place.


**A gateway does not put your catalog in any assistant.** It translates between protocols and controls who gets through, but it does not decide which agent finds you or which store it recommends. agentgateway says it of itself: it assumes the MCP servers, tools and agents it gives access to already exist.[^agentgateway-faq] If the data behind it is incomplete, the gateway serves it just as incomplete, only in more protocols.


## How to check it

1. **See which protocols your store already declares.** If your platform publishes a UCP profile, `/.well-known/ucp` lists the checkout service's transports and the address of each.[^ucp-overview]
2. **Ask your payment provider which protocols it covers.** At Stripe, the integration for selling through agents points to UCP or ACP.[^stripe-agentic]
3. **Before exposing an API, make the list of operations.** On a gateway like Azure's they are chosen one by one; start with the read-only ones.[^azure-apim-mcp]
4. **Review the two authentications**: how the agent proves who it is on the way in and which credentials the gateway uses to call your services.[^aws-agentcore-gateway]
5. **Check what gets lost in translation.** If a service is an A2A agent with long tasks, exposing it as an MCP tool only fits the stateless skills.[^a2a-mcp]

## Related concept: MCP server

An [MCP server](/glossary/mcp-server/) offers its own tools, data and templates to AI applications. A protocol gateway sits in front of one or many of those servers, or of APIs that do not speak MCP, and adds what none has on its own: **translation, a single entry point and access rules**.[^agentgateway-faq][^azure-apim-mcp] From the outside, the gateway looks like one more MCP server; on the inside, it routes each call to whoever it belongs to. If you only have one service and it already speaks MCP, you do not need the gateway for that.

To go further, the [agentic commerce reading path](/learn/agentic-commerce/) orders the rest of the protocols, and the entry on the [agent card](/glossary/agent-card/) explains how an A2A agent introduces itself before anyone translates it.