Block and MCP: goose, Square and the AAIF

Block, the company behind Square and Cash App, works on MCP in three ways. It created goose, an open-source AI agent that connects to tools through MCP. It co-founded the Agentic AI Foundation (AAIF), and its Square team publishes an MCP server for the Square API.

Checked against: Block's goose launch announcement on 28 October 2026. eSEOspace did not test Block's products.

At a glance

What Block offers for MCP

goose, the open-source agent

Block's Open Source Program Office announced goose on 28 January 2025. Block said goose connects to systems "using Anthropic's open source Model Context Protocol" and that it had been "collaborating closely with Anthropic to develop this protocol."

In MCP terms, goose is a client. It runs on your machine and calls MCP servers, which goose calls extensions. The goose documentation says it ships as a desktop app, a CLI and an API. It works with 15+ model providers, including Anthropic, OpenAI, Google and Ollama, and lists 70+ extensions.

Per the extensions guide, you can add three kinds:

• Built-in extensions such as Developer and Memory.
• Command-line (stdio) extensions that run a local command.
• Remote extensions over Streamable HTTP.

The docs also cover MCP Apps (interactive screens inside goose Desktop), reusable YAML "recipes" and subagents.

goose moved to the AAIF

goose was one of three founding projects of the AAIF, a directed fund under the Linux Foundation. The Linux Foundation's launch release lists it beside MCP (from Anthropic) and AGENTS.md (from OpenAI).

On 7 April 2026, the goose team announced the move. The repo is now aaif-goose/goose and the docs live at goose-docs.ai.

The AAIF about page lists Block as a Platinum member. It names Block's Erika Rice Scherpelz on the Governing Board and Bradley Axen, "Goose Creator, Principal Engineer," on the Technical Committee. For the bigger picture, see who owns MCP.

The Square MCP server

The Square MCP docs describe a server "hosted by Block as a remote server" at https://mcp.squareup.com/mcp. You can also run it locally with npx square-mcp-server start. Square labels it Beta. Our Square MCP server profile covers its three tools, OAuth and the read-only switch.

A playbook for building MCP servers

Block's engineers published Block's Playbook for Designing MCP Servers on 16 June 2025. The post says Block has built "more than 60 MCP servers." Its advice includes designing tools around workflows, not single API endpoints, and giving each tool one risk level (read-only or write).

Who it's for

• Teams that want an agent they control. goose runs locally and lets you pick the model, which suits teams with model or data rules.
• Square sellers and developers. The Square MCP server lets an AI app read and change Square data.
• MCP server builders. Block's playbook is a practical design reference. Our MCP development service uses the same kind of workflow-first thinking.

Pricing

• goose: Free and open source under the Apache License 2.0, per Block's announcement and the GitHub repo. You still pay your model provider for API use or a subscription.
• Square MCP server: No public pricing. Square's MCP page does not list a separate fee.
• MCP itself: The protocol is free and open source.

Security and trust

• goose runs autonomously by default. The extensions guide says goose "operates autonomously by default." It can run commands and edit files unless you change the permission mode or tool permissions.
• Malware check. goose says it "automatically checks external extensions for known malware before activation."
• Secrets stay out of config. For remote extensions, the docs say the OAuth secret "never goes in the config file."
• Square is beta. Square says remote instances reach production data only. The local server supports DISALLOW_WRITES=true for read-only use.
• Design guidance. Block's playbook says to prefer OAuth with minimal scopes and "Never save tokens or secrets in plaintext files."

For a fuller checklist, see the MCP Guide security section.

Alternatives

• Anthropic and MCP: the company that created MCP, with Claude as a client.
• OpenAI and MCP: the third AAIF co-founder, with MCP in ChatGPT and its developer tools.
• Best MCP clients: a side-by-side look at other apps that connect to MCP servers.

Next step

If you want an open-source agent, try goose with read-only extensions and approvals turned on first. If you sell on Square, start the Square server in Sandbox with writes disabled. Browse more companies in the MCP company directory.

Frequently asked questions