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MCP is Anthropic’s Model Context Protocol — a standard for how LLM agents (Claude, GPT, Gemini) discover and invoke tools exposed by external servers. Sly provides MCP on two surfaces:
  1. The @sly_ai/mcp-server package — runs locally (stdio transport) and gives Claude Desktop, Cursor, or Windsurf direct access to Sly capabilities
  2. Remote MCP over HTTP — Sly-hosted MCP server at /mcp for agents that need remote tool access

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Local MCP server (Claude Desktop, Cursor, etc.)

Install: 
npx @sly_ai/mcp-server install
This adds Sly to your MCP client’s config. Restart the client; Sly tools appear in the tool catalog. Tools exposed:
  • sly_create_account, sly_list_accounts, sly_get_account
  • sly_create_agent, sly_list_agents
  • sly_create_wallet, sly_get_wallet_balance, sly_fund_wallet
  • sly_create_transfer, sly_get_transfer_status
  • sly_create_stream, sly_withdraw_stream
  • sly_ap2_create_mandate, sly_ap2_execute_mandate
  • sly_ucp_create_token, sly_ucp_settle
  • sly_x402_pay, sly_x402_verify
  • sly_a2a_send_task, sly_a2a_list_tasks, sly_a2a_complete_task
See the MCP tool catalog for the full list with schemas.

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Remote MCP over HTTP

For agent runtimes that don’t run locally but can speak MCP, Sly exposes /mcp directly: 
# JSON-RPC over HTTP
curl -X POST https://api.getsly.ai/mcp \
  -H "Authorization: Bearer agent_..." \
  -d '{
    "jsonrpc": "2.0",
    "method": "tools/list",
    "id": 1
  }'
Returns the tool catalog. Invoke a tool: 
curl -X POST https://api.getsly.ai/mcp \
  -H "Authorization: Bearer agent_..." \
  -d '{
    "jsonrpc": "2.0",
    "method": "tools/call",
    "params": {
      "name": "sly_get_wallet_balance",
      "arguments": { "wallet_id": "wal_..." }
    },
    "id": 2
  }'
Supports three transports:
  • POST /mcp — JSON-RPC request/response (default)
  • GET /mcp — Server-Sent Events streaming (for long-running tools)
  • DELETE /mcp/:session_id — Close a session

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Authentication

MCP over HTTP requires one of Sly’s auth methods. Recommended:
  • Agent token (agent_*) — simplest
  • Ed25519 session (sess_*) — production
API keys work but grant too broad a scope for typical agent use cases.

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Tool discovery

Every registered MCP tool has:
  • A stable name (e.g. sly_create_transfer)
  • An inputSchema (JSON Schema)
  • A description optimized for LLM consumption
  • Permission requirements (what KYA tier / scope can invoke it)
Agents receive only the tools their credentials allow them to invoke.

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Scanner MCP (separate server)

Sly also ships an MCP server for the Scanner service — a demand-intelligence tool for merchants and agents. 
npx @sly_ai/scanner-mcp install
Exposes 19 tools for scanning merchants, analyzing protocol adoption, generating readiness reports, and running agent shopping tests. See the scanner docs for detail.

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When to use MCP

  • You’re building an LLM agent that needs to transact (Claude, GPT, local models)
  • You want drop-in tool access rather than calling the REST API manually
  • Your runtime already speaks MCP (Claude Desktop, Cursor, Windsurf, custom agent frameworks)
  • You want automatic permission filtering — MCP server only exposes tools the agent can actually call
For non-LLM integrations (backend services, CI, operational scripts), use the REST API directly.

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MCP tool catalog

The full list of every tool in @sly_ai/mcp-server and scanner MCP is in the MCP catalog. Each entry includes input schema, example invocation, and permission requirements.