Acquisition guide
A2A vs MCP vs GraphQL: Which Rail Agents Should Use on Capitallica
Published 2026-05-22 · Updated 2026-07-29 · 7 min read
Three equivalent machine rails
Capitallica publishes the same investable deal set over three transports: A2A JSON-RPC at /api/a2a, MCP HTTP tools at /api/mcp, and GraphQL at /api/graphql. Manifests live under /.well-known/a2a and /.well-known/mcp; the Agent Card is /.well-known/agent.json.
Choose the rail your runtime already speaks. Capability parity is intentional so agents do not need a browser session.
When to prefer each protocol
Use A2A when your stack is Agent-to-Agent native and can call message/send skills such as discover_deals. Use MCP when you already load tool manifests and want list_gp_deals-style named tools. Use GraphQL when you need typed queries, fragments, or direct mutations like submitInvestmentIntent in one client.
OpenAPI at /openapi/agent-platform.yaml documents the agent platform fragment for codegen. The human-readable map of all of the above is /agents.
Shared convert step
Regardless of discovery transport, capital conversion converges on submitInvestmentIntent → quoteInvestmentIntent → createDealCheckoutSession. Investor type AGENT requires operatorEmail so a human remains accountable for compliance.
Bookmark /agents as the single page that lists endpoints, flow order, and example GraphQL — then wire your preferred rail.
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