AI agent communication protocols compared: MCP vs A2A vs ACP vs ANP vs Pilot — which fits your stack?

TL;DR: These protocols cover different parts of the stack. MCP handles tool and resource access. A2A, ACP, and ANP define application-level agent interaction or discovery. Pilot operates at the network layer with retained-identity addressing, encrypted UDP tunnels, traversal, and peer trust. This guide compares the layers and shows where they compose.

Why AI agent communication protocols matter

Agents fail to connect for predictable reasons: they sit behind NAT, they restart and change IP addresses, they span clouds with no shared network, or they have no way to verify peer identity before accepting a task. The set of AI agent communication protocols that emerged between 2024 and 2026 each solves a different slice of this problem. Choosing the right one — or the right combination — determines whether your agent fleet is reliable in production or brittle in testing.

This comparison covers five protocols: MCP, A2A, ACP, ANP, and Pilot Protocol. Each is described fairly on its own terms. Where they overlap, we note it. Where they compose well, we show how.

Protocol comparison: MCP vs A2A vs ACP vs ANP vs Pilot

MCP — Model Context Protocol

MCP is an open protocol for connecting AI applications to tools and resources through a client-server interface. An MCP server can expose tools, resources, and prompts. Current standard transports include standard I/O and Streamable HTTP.

MCP is excellent at what it targets: structured, schema-validated tool calls from a single model context. It is not a network protocol. It has no concept of agent addressing, NAT traversal, or agent-to-agent transport. Two MCP servers cannot discover or call each other natively.

Pilot ships a pilot-mcp bridge that runs an MCP server over Pilot's encrypted tunnels, so MCP tools become reachable across NAT without any changes to your MCP logic.

A2A — Agent-to-Agent Protocol

A2A defines how agents communicate at the application layer. Agent Cards can describe capabilities, skills, supported interfaces, and security requirements. Clients then use a supported interface to exchange tasks and messages.

A2A handles collaboration semantics such as task lifecycle and capability advertisement. Its interfaces still need a reachable route, which may be public ingress, a private network, a proxy, or an overlay. Pilot can supply a retained-identity address and encrypted route when the existing deployment does not already provide one.

ACP — Agent Communication Protocol

ACP is a Linux Foundation / BeeAI open standard for REST-based agent interoperability. It supports multi-modal content types and both synchronous and asynchronous messaging patterns. ACP is designed to make agents from different frameworks interoperable over HTTP without imposing a specific runtime.

ACP does not include an overlay network, address assignment, or NAT traversal. It assumes agents are reachable over standard HTTP infrastructure.

ANP — Agent Network Protocol

ANP focuses on decentralized agent identity using DIDs (Decentralized Identifiers) as the anchor. It defines discovery and communication over HTTP transport, designed for scenarios where agents span organizations and cannot rely on a shared registry or trust authority.

ANP is useful when cross-organizational identity and verifiable credentials are the primary concern. Like the other HTTP-based protocols, it assumes reachable endpoints and does not address NAT.

Pilot Protocol — network citizenship for agents

Pilot Protocol operates at the network layer rather than the application layer. It gives every agent three things the HTTP-based protocols assume but do not provide: a permanent address, an encrypted tunnel, and a resolved trust relationship with each peer.

Addressing. Each agent uses a 48-bit virtual address that can remain stable across restarts and IP changes when its cryptographic identity is retained.

Transport. Connections use encrypted UDP tunnels with X25519 key exchange and AES-GCM encryption. Reliability is implemented in userspace over UDP, so the stack runs anywhere without kernel modules.

NAT traversal. Pilot uses STUN for endpoint discovery, coordinated UDP hole-punching for direct-path attempts, and encrypted relay fallback when a direct connection is not available.

Trust. Pilot uses an explicit per-peer mutual approval handshake. Joining the network does not grant access to any peer — each relationship must be approved by both sides. This is a deliberate difference from VPN models where membership implies connectivity.

Discovery. Agents register with a rendezvous registry and a nameserver. Peers can resolve addresses and capabilities without a central broker owning the trust decision.

Pilot is written in Go and ships as static, CGO-free components, is open source under AGPL-3.0, and is available at github.com/pilot-protocol. SDKs are available for Go, Python (pilotprotocol on PyPI), Node, and Swift. The public metric tracks cumulative registered addresses rather than unique active agents or customers.

The Pilot app store: capabilities as IPC services

Pilot ships an app store for installable capability apps. Each app runs locally as a typed IPC service — JSON in, JSON out — and is auto-spawned when installed. Apps include AEGIS (prompt-injection firewall), cosift (grounded web search), sixtyfour (people & company intelligence), miren (PaaS deploys), otto (browser automation), plainweb (web page → Markdown), slipstream (Polymarket smart-money signals), smol (hardware-isolated microVMs), and wallet (on-overlay USDC payments).

The discover → install → call loop takes three commands:

# Discover available apps in the Pilot app store
pilotctl appstore list

# Install a capability app (example: plainweb, web page → Markdown)
pilotctl appstore install io.pilot.plainweb

# Call the installed app via typed IPC (appstore call   [json])
pilotctl appstore call io.pilot.plainweb plainweb.help '{}'

Each installed app becomes a local IPC endpoint your agent can call with a typed JSON request. No HTTP server, no port management, no dependency wrangling.

Which protocol should you use?

The protocols operate at different layers and are not mutually exclusive. A practical production stack often combines them:

• Use MCP when your primary need is giving an LLM access to structured tools and resources. Pair with pilot-mcp if those tools need to be reachable across NAT.
• Use A2A when agents need to delegate tasks to each other using a standardized capability advertisement format. Pair with Pilot for the transport layer when agents are not behind stable public endpoints.
• Use ACP when you need REST-based interop across agent frameworks with multi-modal content support.
• Use ANP when cross-organizational agent identity and DID-based verifiable credentials are the primary concern.
• Use Pilot Protocol when you need agents to maintain stable addresses, traverse NAT, and communicate over encrypted tunnels with explicit per-peer trust — regardless of which application-layer protocol sits on top. See how P2P agent discovery works for a deeper look at the discovery and trust side.

A practical cross-cloud deployment can run Pilot as the network layer with one or more application-layer protocols on top, while keeping application authorization and governance in the surrounding system.

Get started with Pilot Protocol

Install Pilot in one command and have your first agent connected in minutes:

curl -fsSL https://pilotprotocol.network/install.sh | sh

After installation, run pilotctl appstore list to see available capability apps, then pilotctl appstore install <app> to add them to your agent. The GitHub repository has the full source, SDK documentation, and integration guides for MCP and A2A.