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

A developer created an AI agent that triages pitch-deck emails using LangGraph and Nango. The agent reads Gmail attachments, evaluates them against an investment thesis with an LLM, and posts matches to Slack. Nango handles OAuth and exposes Gmail and Slack actions as MCP tools for the graph.

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 https://nango.dev handles the Gmail and Slack connections and exposes them to the graph over MCP. By the end you will have: { fit, reasoning, evidenceQuote } verdict grounded in a real quote from the deck. 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. 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 server at https://api.nango.dev/mcp . Your graph calls those tools by name; no model ever picks them. list-pitch-emails action fetch-attachment action send-slack-message action Go to app.nango.dev/signup https://app.nango.dev/signup and create a free account. Once you're in, open Environment settings in the left sidebar, select the API Keys tab, and copy the key for the dev environment. You'll use this same value in two places later: NANGO SECRET KEY DEV for the CLI, and NANGO SECRET KEY for the graph. An integration is a provider Gmail, Slack plus its OAuth app. Nango ships a shared dev OAuth app for each, so you don't have to register your own. Repeat for Slack . When both exist, your Integrations list looks like this - note the IDs google-mail and slack , which you'll pass to the graph later: Each integration now needs one authorized connection. Do the same on the Slack integration. When you authorize Slack, pick or create the channel you want notifications in - for example pitch-triage - and make sure the Nango app is a member of it. Copy both connection IDs from the Connections tab. You now have: a Nango secret key, a Gmail connection ID, and a Slack connection ID. Create the project and an integration folder for the Nango actions: mkdir -p pitch-deck-triage-agent/integration/.nango cd pitch-deck-triage-agent/integration Create package.json : { "name": "nango-integrations", "version": "1.0.0", "private": true, "type": "module", "engines": { "node": " =22.22.2" }, "scripts": { "compile": "nango compile", "dev": "nango dev" }, "devDependencies": { "nango": "0.71.6", "zod": "4.3.6" } } Install: npm install Create tsconfig.json Nango uses this to type-check your actions : { "$schema": "https://json.schemastore.org/tsconfig", "include": "index.ts", " / .ts" , "exclude": "node modules", "dist", "build", ".nango" , "compilerOptions": { "module": "node16", "target": "esnext", "strict": true, "esModuleInterop": true, "skipLibCheck": true, "moduleResolution": "node16", "exactOptionalPropertyTypes": true, "noUncheckedIndexedAccess": true, "noUnusedLocals": true, "noUnusedParameters": true, "noEmit": true } } Create index.ts - it just imports every action so Nango picks them up note the .js extension even though the files are .ts ; that's the Node 16 module convention Nango uses : import './google-mail/actions/list-pitch-emails.js'; import './google-mail/actions/fetch-attachment.js'; import './slack/actions/send-slack-message.js'; Create .env with the dev secret key you copied earlier: NANGO SECRET KEY DEV=your-nango-dev-secret-key This action searches Gmail for recent messages with a PDF attachment and returns one candidate per message - metadata plus an attachmentId , not the file itself Gmail won't give you both in one call . Create google-mail/actions/list-pitch-emails.ts : js import { createAction } from 'nango'; import as z from 'zod'; // Input is z.object {} .strict , not z.void : Nango compiles void to a // {"type":"null"} schema, but an MCP tools/call sends arguments as an // object {} for a no-input tool , which fails that schema. See Common issues. const QUERY = 'has:attachment filename:pdf newer than:30d'; const MAX RESULTS = 5; const outputSchema = z.object { candidates: z.array z.object { messageId: z.string , threadId: z.string , from: z.string , subject: z.string , attachmentId: z.string , filename: z.string } } ; interface GmailHeader { name: string; value: string; } interface GmailPart { mimeType?: string; filename?: string; body?: { attachmentId?: string; size?: number }; parts?: GmailPart ; } interface GmailMessage { id: string; threadId: string; payload?: GmailPart & { headers?: GmailHeader }; } interface GmailListResponse { messages?: { id: string; threadId: string } ; } function findPdfAttachment part: GmailPart | undefined : { attachmentId: string; filename: string } | undefined { if part { return undefined; } if part.mimeType === 'application/pdf' && part.body?.attachmentId { return { attachmentId: part.body.attachmentId, filename: part.filename || 'deck.pdf' }; } for const child of part.parts ?? { const found = findPdfAttachment child ; if found { return found; } } return undefined; } function header headers: GmailHeader | undefined, name: string : string { return headers?.find h = h.name.toLowerCase === name.toLowerCase ?.value ?? ''; } const action = createAction { description: 'List recent Gmail messages that have a PDF attachment, one candidate Pitch Deck per message.', version: '1.0.0', endpoint: { method: 'GET', path: '/gmail/pitch-emails', group: 'Triage' }, input: z.object {} .strict , output: outputSchema, exec: async nango : Promise<z.infer<typeof outputSchema = { const listRes = await nango.get<GmailListResponse { endpoint: '/gmail/v1/users/me/messages', params: { q: QUERY, maxResults: String MAX RESULTS } } ; const candidates: z.infer<typeof outputSchema 'candidates' = ; for const { id } of listRes.data.messages ?? { const msgRes = await nango.get<GmailMessage { endpoint: /gmail/v1/users/me/messages/${id} , params: { format: 'full' } } ; const attachment = findPdfAttachment msgRes.data.payload ; if attachment { continue; } candidates.push { messageId: msgRes.data.id, threadId: msgRes.data.threadId, from: header msgRes.data.payload?.headers, 'From' , subject: header msgRes.data.payload?.headers, 'Subject' , attachmentId: attachment.attachmentId, filename: attachment.filename } ; } return { candidates }; } } ; export type NangoActionLocal = Parameters< typeof action 'exec' 0 ; export default action; Inside exec , nango.get calls the real Gmail API with the connection's token attached for you. You never see a token. Given the messageId and attachmentId from the first action, this one downloads the attachment's bytes. Create google-mail/actions/fetch-attachment.ts : js import { createAction } from 'nango'; import as z from 'zod'; const inputSchema = z.object { messageId: z.string .min 1 , attachmentId: z.string .min 1 } ; const outputSchema = z.object { // Gmail returns this base64url-encoded - and instead of + and / , // not standard base64. The caller converts before decoding. data: z.string , size: z.number } ; interface GmailAttachmentResponse { data: string; size: number; } const action = createAction { description: "Fetch the raw content of one Gmail attachment base64url-encoded, as Gmail's API returns it .", version: '1.0.0', endpoint: { method: 'GET', path: '/gmail/attachment', group: 'Triage' }, input: inputSchema, output: outputSchema, exec: async nango, input : Promise<z.infer<typeof outputSchema = { const res = await nango.get<GmailAttachmentResponse { endpoint: /gmail/v1/users/me/messages/${input.messageId}/attachments/${input.attachmentId} } ; return { data: res.data.data, size: res.data.size }; } } ; export type NangoActionLocal = Parameters< typeof action 'exec' 0 ; export default action; This one posts to Slack's chat.postMessage . Slack answers HTTP 200 even when a post fails, with the real error in { ok: false, error } - Nango's retry logic keys off status codes and never sees that, so the action checks ok itself. Create slack/actions/send-slack-message.ts : js import { createAction } from 'nango'; import as z from 'zod'; const inputSchema = z.object { channel: z.string .min 1 .describe 'Slack channel ID or name e.g. " pitch-triage" ' , text: z.string .min 1 } ; const outputSchema = z.object { channel: z.string , ts: z.string } ; interface SlackPostMessageResponse { ok: boolean; error?: string; channel?: string; ts?: string; } const action = createAction { description: 'Post a message to a Slack channel.', version: '1.0.0', endpoint: { method: 'POST', path: '/slack/messages', group: 'Triage' }, input: inputSchema, output: outputSchema, exec: async nango, input : Promise<z.infer<typeof outputSchema = { const res = await nango.post<SlackPostMessageResponse { endpoint: '/chat.postMessage', retries: 0, data: { channel: input.channel, text: input.text } } ; if res.data.ok || res.data.ts || res.data.channel { throw new nango.ActionError { message: Slack chat.postMessage failed: ${res.data.error ?? 'unknown error'} } ; } return { channel: res.data.channel, ts: res.data.ts }; } } ; export type NangoActionLocal = Parameters< typeof action 'exec' 0 ; export default action; From the integration folder: npx nango deploy dev Nango type-checks and uploads all three actions in one go: Check the Functions tab on each integration in the dashboard. Gmail shows list-pitch-emails and fetch-attachment : Slack shows send-slack-message : Each deployed action is now also a tool on Nango's MCP server. That's what the graph calls next. Back at the project root, create a graph folder for the pipeline: cd .. mkdir -p graph/src cd graph { "name": "pitch-deck-triage-graph", "version": "1.0.0", "private": true, "type": "module", "engines": { "node": " =22" }, "scripts": { "triage": "tsx src/run.ts", "generate-decks": "tsx src/generate-decks.ts" }, "dependencies": { "@langchain/langgraph": "^0.2.57", "dotenv": "^16.4.5", "openai": "^4.104.0", "pdfjs-dist": "^6.3.289" }, "devDependencies": { "@types/node": "^22.9.0", "@types/pdfkit": "^0.13.4", "pdfkit": "^0.15.1", "tsx": "^4.19.2", "typescript": "^5.6.3" } } npm install Create tsconfig.json : { "compilerOptions": { "target": "es2022", "module": "node16", "moduleResolution": "node16", "strict": true, "esModuleInterop": true, "skipLibCheck": true, "noEmit": true, "allowImportingTsExtensions": true, "types": "node" }, "include": "src/ / .ts" } Create .env with the values you gathered earlier NANGO SECRET KEY is the same dev key as NANGO SECRET KEY DEV : OPENAI API KEY=your-openai-key NANGO SECRET KEY=your-nango-dev-secret-key NANGO GMAIL CONNECTION ID=your-gmail-connection-id NANGO SLACK CONNECTION ID=your-slack-connection-id SLACK CHANNEL=" pitch-triage" Quote SLACK CHANNEL if it starts with - dotenv treats an unquoted as a comment and drops the rest of the line. Four small src/ files the pipeline depends on. src/thesis.ts - the fixed rule every deck is judged against. Edit it to match a real thesis if you like; this one is fabricated. js export const THESIS = Acme Ventures invests in seed-stage, developer-focused B2B software companies. We look for: - US or EU-incorporated companies - A product built for a technical buyer developers, DevOps, IT, or security teams - $0-$2M in current ARR - At least one technical co-founder who still writes code - A believable path to $1M ARR within 12 months of this round We do not invest in consumer apps, hardware, life sciences, gaming, or crypto/token-based businesses, regardless of traction. ; src/mcp-client.ts - a ~100-line client no SDK that calls one named tool on Nango's MCP server. It does the MCP handshake initialize , then notifications/initialized , then tools/call and unwraps the result. Each call carries three headers so Nango knows which account to use: your secret key, the connection-id , and the provider-config-key google-mail or slack . js const NANGO MCP URL = 'https://api.nango.dev/mcp'; export interface McpScope { connectionId: string; providerConfigKey: string; } interface JsonRpcResponse { jsonrpc: '2.0'; id?: number; result?: unknown; error?: { code: number; message: string; data?: unknown }; } interface McpToolResult { isError?: boolean; content?: { type: string; text?: string } ; } function headersFor secretKey: string, scope: McpScope : Record<string, string { return { 'Content-Type': 'application/json', Accept: 'application/json, text/event-stream', Authorization: Bearer ${secretKey} , 'connection-id': scope.connectionId, 'provider-config-key': scope.providerConfigKey }; } async function parseBody res: Response : Promise<JsonRpcResponse | undefined { const contentType = res.headers.get 'content-type' ?? ''; const body = await res.text ; if body { return undefined; } if contentType.includes 'text/event-stream' { // SSE framing: one or more "data: <json " lines; take the last. const dataLines = body .split '\n' .filter line = line.startsWith 'data:' .map line = line.slice 'data:'.length .trim ; const last = dataLines.at -1 ; return last ? JSON.parse last as JsonRpcResponse : undefined; } return JSON.parse body as JsonRpcResponse; } let nextId = 1; async function rpc headers: Record<string, string , method: string, params?: unknown : Promise<unknown { const res = await fetch NANGO MCP URL, { method: 'POST', headers, body: JSON.stringify { jsonrpc: '2.0', id: nextId++, method, params } } ; if res.ok { throw new Error MCP ${method} failed: HTTP ${res.status} ${await res.text } ; } const parsed = await parseBody res ; if parsed?.error { throw new Error MCP ${method} error: ${JSON.stringify parsed.error } ; } return parsed?.result; } export async function callNangoTool<T = unknown secretKey: string, scope: McpScope, toolName: string, args: Record<string, unknown : Promise<T { const headers = headersFor secretKey, scope ; await rpc headers, 'initialize', { protocolVersion: '2025-03-26', capabilities: {}, clientInfo: { name: 'pitch-deck-triage-graph', version: '1.0.0' } } ; // Required notification - no response expected, fire and ignore. await fetch NANGO MCP URL, { method: 'POST', headers, body: JSON.stringify { jsonrpc: '2.0', method: 'notifications/initialized' } } .catch = undefined ; const result = await rpc headers, 'tools/call', { name: toolName, arguments: args } as McpToolResult | undefined; if result?.isError { throw new Error Nango tool "${toolName}" failed: ${JSON.stringify result.content } ; } const textBlock = result?.content?.find c = c.type === 'text' && typeof c.text === 'string' ; if textBlock?.text { throw new Error Nango tool "${toolName}" returned no text content: ${JSON.stringify result } ; } return JSON.parse textBlock.text as T; } src/pdf.ts - turns the base64url bytes from fetch-attachment into plain text. It uses pdfjs-dist directly the older pdf-parse package chokes on PDFs from a current pdfkit . Text only, no OCR - an image-only deck comes back empty. js import { getDocument } from 'pdfjs-dist/legacy/build/pdf.mjs'; interface TextItem { str?: string; } type GetDocumentParams = Parameters<typeof getDocument 0 ; export async function extractPdfText base64UrlData: string : Promise<string { const base64 = base64UrlData.replace /-/g, '+' .replace / /g, '/' ; const buffer = Buffer.from base64, 'base64' ; // disableWorker isn't in this version's types but works at runtime. const params = { data: new Uint8Array buffer , disableWorker: true } as unknown as GetDocumentParams; const doc = await getDocument params .promise; const pages: string = ; for let pageNum = 1; pageNum <= doc.numPages; pageNum++ { const page = await doc.getPage pageNum ; const content = await page.getTextContent ; const text = content.items.map item = item as TextItem .str ?? '' .join ' ' ; pages.push text ; } return pages.join '\n\n' .trim ; } src/assess.ts - the only LLM call in the whole project. One OpenAI Structured Outputs call returns { fit, reasoning, evidenceQuote } . The schema forces evidenceQuote to be one contiguous span from the deck - without that, the model stitched two non-adjacent sentences together with "..." and called it a quote. python import type OpenAI from 'openai'; export interface FitAssessment { fit: boolean; reasoning: string; evidenceQuote: string; } const SCHEMA = { type: 'object', properties: { fit: { type: 'boolean', description: 'True if the deck matches the thesis, false otherwise.' }, reasoning: { type: 'string', description: 'One or two sentences explaining the fit/no-fit call.' }, evidenceQuote: { type: 'string', description: "A single contiguous verbatim span copied from the deck's text a sentence or clause, not several stitched together with '...' that the reasoning is grounded in." } }, required: 'fit', 'reasoning', 'evidenceQuote' , additionalProperties: false } as const; export async function assessFit openai: OpenAI, thesis: string, deckText: string : Promise<FitAssessment { const response = await openai.responses.create { model: 'gpt-4.1', // pin the current model at build time input: { role: 'system', content: "You triage pitch decks against a fixed investment thesis. Judge only what the deck's text actually says - don't assume anything it doesn't state. Ground your reasoning in one short, verbatim quote from the deck: a single contiguous span copied exactly as written, never several sentences stitched together with '...'." }, { role: 'user', content: Thesis:\n${thesis}\n\nPitch deck text:\n${deckText} } , text: { format: { type: 'json schema', name: 'fit assessment', schema: SCHEMA, strict: true } } } ; return JSON.parse response.output text as FitAssessment; } Now the graph itself. Four nodes in a line, with two exits: stop if no candidate email, stop if the deck doesn't fit. No model chooses tools - each node calls one named Nango tool. Create src/pipeline.ts : js import { StateGraph, Annotation, START, END } from '@langchain/langgraph'; import type OpenAI from 'openai'; import { callNangoTool } from './mcp-client.ts'; import { extractPdfText } from './pdf.ts'; import { assessFit, type FitAssessment } from './assess.ts'; import { THESIS } from './thesis.ts'; interface EmailCandidate { messageId: string; threadId: string; from: string; subject: string; attachmentId: string; filename: string; } const TriageState = Annotation.Root { email: Annotation<EmailCandidate | null { reducer: prev, next = next, default: = null } , deckText: Annotation<string | null { reducer: prev, next = next, default: = null } , assessment: Annotation<FitAssessment | null { reducer: prev, next = next, default: = null } , notified: Annotation<boolean { reducer: prev, next = next, default: = false } } ; export interface GraphConfig { nangoSecretKey: string; gmailConnectionId: string; slackConnectionId: string; slackChannel: string; openai: OpenAI; } export function buildTriageGraph config: GraphConfig { const gmailScope = { connectionId: config.gmailConnectionId, providerConfigKey: 'google-mail' }; const slackScope = { connectionId: config.slackConnectionId, providerConfigKey: 'slack' }; const graph = new StateGraph TriageState .addNode 'fetchEmail', async = { const { candidates } = await callNangoTool<{ candidates: EmailCandidate } config.nangoSecretKey, gmailScope, 'list-pitch-emails', {} ; const email = candidates 0 ?? null; if email { console.log 'No candidate Pitch Deck email found - nothing to triage this run.' ; } return { email }; } .addNode 'fetchDeck', async state = { if state.email { return {}; } const { data } = await callNangoTool<{ data: string; size: number } config.nangoSecretKey, gmailScope, 'fetch-attachment', { messageId: state.email.messageId, attachmentId: state.email.attachmentId } ; const deckText = await extractPdfText data ; return { deckText }; } .addNode 'assess', async state = { if state.deckText { return {}; } const assessment = await assessFit config.openai, THESIS, state.deckText ; return { assessment }; } .addNode 'notify', async state = { if state.email || state.assessment { return {}; } const text = Pitch deck fit — ${state.email.subject} from ${state.email.from} \n + Fit: ${state.assessment.fit ? '✅ yes' : '❌ no'}\n + Reasoning: ${state.assessment.reasoning}\n + ${state.assessment.evidenceQuote} ; await callNangoTool config.nangoSecretKey, slackScope, 'send-slack-message', { channel: config.slackChannel, text } ; return { notified: true }; } .addEdge START, 'fetchEmail' .addConditionalEdges 'fetchEmail', state = state.email ? 'fetchDeck' : END , { fetchDeck: 'fetchDeck', END : END } .addEdge 'fetchDeck', 'assess' .addConditionalEdges 'assess', state = state.assessment?.fit ? 'notify' : END , { notify: 'notify', END : END } .addEdge 'notify', END ; return graph.compile ; } Create src/run.ts - it reads the .env , builds the graph, and runs it once: python import 'dotenv/config'; import OpenAI from 'openai'; import { buildTriageGraph } from './pipeline.ts'; function requireEnv name: string : string { const v = process.env name ; if v { throw new Error Missing env var ${name} - see .env.example ; } return v; } const openai = new OpenAI { apiKey: requireEnv 'OPENAI API KEY' } ; const graph = buildTriageGraph { nangoSecretKey: requireEnv 'NANGO SECRET KEY' , gmailConnectionId: requireEnv 'NANGO GMAIL CONNECTION ID' , slackConnectionId: requireEnv 'NANGO SLACK CONNECTION ID' , slackChannel: requireEnv 'SLACK CHANNEL' , openai } ; const started = Date.now ; const result = await graph.invoke {} ; const elapsed = Date.now - started; console.log \n--- Triage Run ${elapsed} ms --- ; console.log JSON.stringify result, null, 2 ; You need PDFs to test with. Create src/generate-decks.ts - it writes three fabricated decks one that fits the thesis, two that don't : python import PDFDocument from 'pdfkit'; import { createWriteStream, mkdirSync } from 'node:fs'; import { join, dirname } from 'node:path'; import { fileURLToPath } from 'node:url'; const dirname = dirname fileURLToPath import.meta.url ; const OUT DIR = join dirname, '..', '..', 'decks' ; interface Deck { filename: string; lines: string ; } const DECKS: Deck = { filename: 'quantumleap-fit.pdf', lines: 'QuantumLeap Analytics', 'Observability for backend engineers, not SREs on-call at 3am.', '', 'Problem: mid-size engineering teams drown in dashboards but still get paged for issues nobody can explain.', 'Solution: a query-log-first observability tool built directly into the deploy pipeline, no agent to babysit.', '', 'Team: two co-founders, both ex-Datadog engineers, both still write the core query engine.', 'Traction: $380K ARR across 14 mid-market engineering teams, up from $90K six months ago.', 'Ask: raising a $2.5M seed to hire 2 engineers and close a pipeline of 6 enterprise pilots we believe gets us to $1.1M ARR within 12 months.', 'Incorporated: Delaware C-corp, HQ in Austin, TX.' }, { filename: 'fieldnote-no-fit-consumer.pdf', lines: 'Fieldnote', 'A daily journaling app that turns your mood into a photo memory.', '', 'Problem: people want to reflect on their day but journaling apps feel like homework.', 'Solution: a 10-second voice note becomes a journal entry with an AI-generated photo of your mood.', '', 'Team: one founder, background in product design at a consumer social app.', 'Traction: 40,000 downloads, 3,200 weekly active users, freemium with a $4.99/mo tier.', 'Ask: raising a $1.5M pre-seed to grow to 250,000 downloads via TikTok creator partnerships.', 'Incorporated: Delaware C-corp, HQ in Los Angeles, CA.' }, { filename: 'brightforge-no-fit-hardware.pdf', lines: 'BrightForge Robotics', 'Autonomous forklifts for mid-size warehouses.', '', "Problem: mid-size warehouses can't justify a full automation retrofit, so they stay manual and understaffed.", 'Solution: a retrofit kit that turns an existing forklift into an autonomous unit in under a day.', '', 'Team: two mechanical engineers, one ex-Boston Dynamics, one ex-Zoox.', 'Traction: 3 warehouse pilots running, $210K in signed pilot revenue, hardware gross margin 38%.', 'Ask: raising a $4M seed to build the next hardware revision and open a small assembly line.', 'Incorporated: Delaware C-corp, HQ in Pittsburgh, PA.' } ; mkdirSync OUT DIR, { recursive: true } ; async function writeDeck deck: Deck : Promise<void { const outPath = join OUT DIR, deck.filename ; const doc = new PDFDocument { margin: 60 } ; const stream = createWriteStream outPath ; doc.pipe stream ; const title, ...rest = deck.lines; doc.fontSize 20 .text title ?? '', { underline: true } ; doc.moveDown ; doc.fontSize 12 ; for const line of rest { if line === '' { doc.moveDown ; } else { doc.text line ; } } doc.end ; // pdfkit flushes the trailer asynchronously - wait for the stream to // finish or the file is truncated. await new Promise<void resolve, reject = { stream.on 'finish', resolve ; stream.on 'error', reject ; } ; console.log Wrote ${outPath} ; } for const deck of DECKS { await writeDeck deck ; } Run it: npm run generate-decks Three PDFs land in decks/ at the project root. decks/quantumleap-fit.pdf to the Gmail account you connected, as a PDF attachment. Any subject line. graph folder: npm run triage The pipeline searches your inbox, downloads the PDF, extracts its text, asks OpenAI for a verdict, and - because this deck fits the thesis - posts to Slack: The console prints the full state, including the assessment: { "email": { "subject": "pitch deck", "from": "you@gmail.com", "filename": "quantumleap-fit.pdf", ... }, "assessment": { "fit": true, "reasoning": "US incorporation, developer-focused B2B software, ARR in range, technical co-founders coding, clear path to $1M+ ARR in 12 months.", "evidenceQuote": "Team: two co-founders, both ex-Datadog engineers, both still write the core query engine." }, "notified": true } Now email fieldnote-no-fit-consumer.pdf and run it again: same fetch and extract, but the assessment comes back fit: false "a consumer journaling app, not B2B software for technical buyers" , the graph routes past notify , and no Slack message is sent. | Issue | Cause and fix | |---|---| | invalid action input: must be null when a no-input action is called over MCP | Nango compiles a z.void input schema to {"type":"null"} , but an MCP tools/call always sends arguments as an object {} for a no-input tool , which fails that schema. Use z.object {} .strict instead of z.void . | | SLACK CHANNEL reads as empty despite being set in .env | dotenv treats an unquoted as a comment marker and drops everything after it, so SLACK CHANNEL= pitch-triage becomes empty. Quote it: SLACK CHANNEL=" pitch-triage" . | | nango deploy dev removes actions from another project | nango deploy makes the environment match the folder you deploy from - it's scoped to the environment, not the folder. Deploying a second project against the same secret key can wipe the first project's actions. Use a separate Nango environment per project. | | A run picks the wrong email when several are waiting | Gmail's messages.list order is not reliably newest-first. Code that takes candidates 0 can act on an older message while a newer one waits behind it. Sort or filter on internalDate rather than trusting order. | | Running the same pipeline twice on one email sends two Slack messages | Nothing remembers what was already processed. A search-based trigger needs its own idempotency key, checked and stored somewhere durable, if re-runs shouldn't double-notify. | | The extracted deck text is empty | The PDF has no text layer it's a slide export of images . This pipeline is text-only, no OCR. | The pipeline is short because Nango absorbs the parts that usually aren't: two OAuth flows, token refresh, the base URL and auth header on every provider call, and a tool interface the graph can call without an SDK. What's left in your code is the actual triage logic - search, extract, judge, notify - and a fixed graph wiring it together. The same shape works for any "read an inbox, judge it against a rule, tell a channel" task: support triage, lead routing, compliance review. Swap the thesis, the Gmail query, and the Slack text. Full code: github.com/emmakodes/pitch-deck-triage-agent https://github.com/emmakodes/pitch-deck-triage-agent . Built with Nango https://nango.dev , LangGraph https://langchain-ai.github.io/langgraphjs/ , and the OpenAI Structured Outputs API.