How to build a pitch deck triage agent with LangGraph and Nango

In this guide you will build an AI agent that reads pitch-deck emails from Gmail, judges each deck against a fixed investment thesis with an LLM, and posts a Slack message when a deck is a fit. LangGraph orchestrates the steps; Nango handles the Gmail and Slack connections and exposes them to the graph over MCP. By the end you will have: Three Nango actions - search Gmail for pitch-deck emails, download an attachment, post to Slack - deployed and callable. A LangGraph pipeline that runs those actions in a fixed order and, in between, asks OpenAI for a { fit, reasoning, evidenceQuote } verdict grounded in a real quote from the deck. A working end-to-end run: email a PDF to yourself, run one command, get a Slack message. Why is it hard to build a pipeline like this? You need two separate OAuth integrations - Gmail and Slack - each with its own token lifecycle, scopes, and refresh flow. Get either wrong and the pipeline fails days later when a token expires, not on your first test. Gmail's API does not hand you a pitch deck in one call. Searching an inbox returns message metadata; getting an attachment's bytes is a second request keyed off an attachmentId from the first. And Gmail returns those bytes base64url-encoded, not standard base64, so a naive decode produces a broken PDF. Then there's the LLM. It's easy to get a model to say "yes, this fits". It's harder to make it say why , and prove the why by quoting the actual document rather than paraphrasing something half-remembered from the prompt. Why use Nango for this Nango gives you the OAuth flow, token storage, and refresh logic for Gmail and Slack out of the box. You connect an account once in a hosted popup; every call after that carries a valid token without your code touching it. You write the provider logic as small server-side functions called actions - input schema, output schema, and an exec body. Deploy one and it's a versioned endpoint, and Nango automatically exposes it as a tool on its hosted MCP serve