Block basics

Every block declares its input and output ports with a data type: trigger, text, json, vector, blob, or the permissive any. A connection is only valid between an output and an input whose types agree, and the composer canvas checks this the moment you draw the wire — the same check POST /flows/:id/versions runs server-side, so a graph that renders on the canvas is a graph the API accepts.

• http_trigger — no inputs, one json output; where a request enters the graph.
• workers_ai — text in, text out; runs a prompt through a hosted model.
• ai_gateway — json in, json out; routes the same call through a proxy with caching and retries.
• vectorize — text in, vector out; upserts or queries the vector index.
• r2, queues, agents, ai_search, mcp, session_memory, http — one json port each way, wrapping the Cloudflare service or external call the name says.

The full definition of every block — its ports, its category and what it wraps — is in the glossary, one entry per block or per service it is built on. Start at Flow and Block; each entry links to the ones it composes with.