Teams App Developer

link-unfurl-preview-ts

purpose

Bridges Slack link unfurling (link_shared, chat.unfurl) and Teams link preview (messageHandlers) for cross-platform bots targeting Slack, Teams, or both.

rules

1. Slack app.event('link_shared') + chat.unfurl() → Teams message.ext.query-link handler. Slack fires a link_shared event and the bot calls chat.unfurl() asynchronously. Teams uses a compose extension handler that must return the unfurl card synchronously. The handler name in the Teams SDK is message.ext.query-link (or the equivalent composeExtension/queryLink activity). learn.microsoft.com -- Link unfurling

2. Manifest composeExtensions[].messageHandlers with domain list is required. Unlike Slack where you register unfurl domains in the app dashboard, Teams requires them in the manifest JSON under composeExtensions[0].messageHandlers[0].value.domains. Only URLs matching these domains trigger unfurling. learn.microsoft.com -- Manifest schema

3. Teams has a 5-second synchronous response deadline. Slack's link_shared event allows async unfurling — the bot receives the event, processes it, then calls chat.unfurl() within 30 minutes. Teams' query-link is an invoke that must return the preview card within ~5 seconds. If data fetching takes longer, return a minimal card and cannot update later. learn.microsoft.com -- Link unfurling

4. The bot must be installed in the conversation for unfurling to work. Slack link unfurling works in any channel where the app is installed (workspace-level). Teams link unfurling only works in conversations where the bot is explicitly installed. Users may need to @mention the bot or add it to the team/chat first. learn.microsoft.com -- Link unfurling prerequisites

5. No retroactive unfurling of already-posted links. Slack can unfurl links in messages already posted (if the app is added later). Teams only unfurls links at the time they are composed/sent. Links in existing messages are never retroactively unfurled. learn.microsoft.com -- Link unfurling

6. Slack unfurl supports multiple links per message; Teams handles one at a time. Slack's link_shared event includes an array of links from the message. Teams invokes the query-link handler once per URL. If a message contains multiple matching URLs, the handler is called multiple times. learn.microsoft.com -- Link unfurling

7. Return an Adaptive Card (not Hero/Thumbnail) for rich previews. Slack unfurls return attachment objects with title, text, thumb_url, color. Teams link unfurling should return Adaptive Cards for the richest preview. The response format wraps the card in a composeExtension result with type: "result". learn.microsoft.com -- Cards in extensions

8. Domain matching is exact — no wildcards for subdomains. Slack unfurl domain matching supports wildcards. Teams manifest messageHandlers.value.domains requires exact domain entries. To match foo.example.com and bar.example.com, list both explicitly. learn.microsoft.com -- Manifest domains

9. Slack's unfurl is_bot_token_only flag → not applicable. Slack distinguishes between user-token and bot-token unfurling. Teams link unfurling always runs as the bot identity. There is no user-token mode. github.com/microsoft/teams.ts

10. Cache unfurl results where possible. Since the 5-second deadline is strict, cache API responses for frequently unfurled URLs. Slack's async model made caching less critical. In Teams, a cache miss that takes >5 seconds means the unfurl silently fails with no preview shown. learn.microsoft.com -- Link unfurling

11. Reverse direction (Teams → Slack): For Teams → Slack, map messageHandlers domain config to link_shared event subscription (configured in the Slack app dashboard under Unfurl Domains), and preview card responses to chat.unfurl calls. The key advantage in reverse is that Slack's async model (chat.unfurl within 30 minutes) is more forgiving than Teams' 5-second synchronous deadline. Adaptive Card preview content maps to Slack unfurl attachment objects with title, text, thumb_url, and color.

patterns

link_shared → query-link handler migration

Slack (before):

import { App } from "@slack/bolt";

const app = new App({
  token: process.env.SLACK_BOT_TOKEN!,
  signingSecret: process.env.SLACK_SIGNING_SECRET!,
});

// Async unfurl — no time pressure
app.event("link_shared", async ({ event, client }) => {
  const unfurls: Record<string, any> = {};

  for (const link of event.links) {
    if (link.domain === "myapp.example.com") {
      const match = link.url.match(/\/issues\/(\d+)/);
      if (match) {
        const issue = await fetchIssue(match[1]); // can take 10+ seconds
        unfurls[link.url] = {
          title: `Issue #${issue.id}: ${issue.title}`,
          text: issue.description,
          color: issue.status === "open" ? "#36a64f" : "#e01e5a",
          thumb_url: issue.assignee?.avatarUrl,
          footer: `Status: ${issue.status}`,
        };
      }
    }
  }

  if (Object.keys(unfurls).length > 0) {
    await client.chat.unfurl({
      ts: event.message_ts,
      channel: event.channel,
      unfurls,
    });
  }
});

Teams (after):

import { App } from "@microsoft/teams.apps";
import { ConsoleLogger } from "@microsoft/teams.common";

const app = new App({
  logger: new ConsoleLogger("my-bot", { level: "info" }),
});

// Simple in-memory cache to meet 5-second deadline
const issueCache = new Map<string, { data: any; expiry: number }>();

// Synchronous unfurl — must respond within 5 seconds
app.on("message.ext.query-link" as any, async ({ activity }) => {
  const url: string = activity.value?.url ?? "";
  const match = url.match(/\/issues\/(\d+)/);

  if (!match) {
    return { status: 200, body: {} }; // No preview for unrecognized URLs
  }

  const issueId = match[1];
  let issue: any;

  // Check cache first (critical for meeting 5-second deadline)
  const cached = issueCache.get(issueId);
  if (cached && cached.expiry > Date.now()) {
    issue = cached.data;
  } else {
    issue = await fetchIssue(issueId);
    issueCache.set(issueId, { data: issue, expiry: Date.now() + 5 * 60_000 });
  }

  const statusColor = issue.status === "open" ? "good" : "attention";

  return {
    status: 200,
    body: {
      composeExtension: {
        type: "result",
        attachmentLayout: "list",
        attachments: [{
          contentType: "application/vnd.microsoft.card.adaptive",
          content: {
            type: "AdaptiveCard",
            version: "1.5",
            body: [
              {
                type: "TextBlock",
                text: `Issue #${issue.id}: ${issue.title}`,
                weight: "Bolder",
                size: "Medium",
              },
              {
                type: "TextBlock",
                text: issue.description,
                wrap: true,
                maxLines: 3,
              },
              {
                type: "ColumnSet",
                columns: [
                  {
                    type: "Column",
                    width: "auto",
                    items: [{
                      type: "TextBlock",
                      text: `Status: **${issue.status}**`,
                      color: statusColor,
                    }],
                  },
                  {
                    type: "Column",
                    width: "stretch",
                    items: [{
                      type: "TextBlock",
                      text: issue.assignee?.name ? `Assigned: ${issue.assignee.name}` : "Unassigned",
                      isSubtle: true,
                      horizontalAlignment: "Right",
                    }],
                  },
                ],
              },
            ],
            actions: [{
              type: "Action.OpenUrl",
              title: "View Issue",
              url,
            }],
          },
          preview: {
            contentType: "application/vnd.microsoft.card.thumbnail",
            content: {
              title: `Issue #${issue.id}: ${issue.title}`,
              text: `Status: ${issue.status}`,
            },
          },
        }],
      },
    },
  };
});

async function fetchIssue(id: string) {
  return { id, title: "Login broken on Safari", description: "Users report...", status: "open", assignee: { name: "Alice", avatarUrl: "" } };
}

app.start(3978);

Manifest domain configuration

Slack — domains are configured in the Slack app dashboard under "Event Subscriptions > Unfurl Domains".

Teams — domains must be in the manifest JSON:

{
  "composeExtensions": [
    {
      "botId": "${{BOT_ID}}",
      "messageHandlers": [
        {
          "type": "link",
          "value": {
            "domains": [
              "myapp.example.com",
              "issues.example.com"
            ]
          }
        }
      ],
      "commands": []
    }
  ]
}

Unfurl mapping table

Cache middleware best practice (Y7)

The 5-second Teams deadline makes caching non-optional. Always use a cache layer for unfurl handlers.

// Reusable cache-first unfurl wrapper
const unfurlCache = new Map<string, { data: any; expires: number }>();

function withUnfurlCache<T>(
  fetchFn: (url: string) => Promise<T>,
  ttlMs: number = 300_000 // 5 min default
) {
  return async (url: string): Promise<T> => {
    const cached = unfurlCache.get(url);
    if (cached && cached.expires > Date.now()) {
      return cached.data as T;
    }
    const data = await fetchFn(url); // must complete in <4 seconds
    unfurlCache.set(url, { data, expires: Date.now() + ttlMs });
    return data;
  };
}

// Usage
const cachedFetchIssue = withUnfurlCache(
  async (url: string) => {
    const id = url.match(/\/issues\/(\d+)/)?.[1];
    return id ? await fetchIssue(id) : null;
  },
  5 * 60_000 // 5 min TTL
);

app.on("message.ext.query-link" as any, async ({ activity }) => {
  const url: string = activity.value?.url ?? "";
  const issue = await cachedFetchIssue(url);
  if (!issue) return { status: 200, body: {} };
  return buildUnfurlResponse(issue);
});

Best practices:

• Set TTL based on data freshness needs (5–60 minutes)

• Pre-populate cache for known high-traffic URLs on startup

• Never make multiple API calls inside the unfurl handler — pre-fetch or batch

• For production, replace the Map with Redis or a shared cache

Don't: Skip caching even for "fast" data sources. Network latency + cold starts can push you past 5 seconds.

Reverse (Teams → Slack): Slack's 30-minute async model makes caching less critical, but still recommended for performance.

pitfalls

• Missing messageHandlers in manifest: Without the messageHandlers array in composeExtensions, link unfurling never triggers. The bot receives no activity for matching URLs. This is the #1 deployment issue for link unfurling.

• 5-second deadline with no fallback: If data fetching exceeds 5 seconds, the unfurl silently fails — no error card, no retry. Users see a plain URL with no preview. Implement aggressive caching and fast-path responses.

• Bot must be installed in the conversation: Unlike Slack where workspace-level app installation enables unfurling everywhere, Teams requires the bot to be installed in each team/chat where unfurling should work. Users may not understand why links aren't unfurling in some conversations.

• No retroactive unfurling: Existing messages with matching URLs are never unfurled when the bot is installed later. Only new messages trigger the handler. Slack supports unfurling existing messages.

• Exact domain matching: *.example.com is not supported. If your app has URLs across app.example.com, api.example.com, and docs.example.com, all three must be listed separately in the manifest. For apps with many subdomains, use a build-time manifest generator script (see Y15 pattern below).

• Adaptive Card size limit: Link preview cards are subject to the standard 28 KB Adaptive Card size limit. Keep previews concise — unfurl cards with embedded images or long descriptions may be silently truncated.

Domain wildcard workaround: manifest generator (Y15)

Teams requires exact domain listing — no wildcards. For apps with many subdomains, automate manifest generation at build time.

// scripts/generate-manifest-domains.ts
import fs from "fs";

// Source of truth: your subdomain list (from config, DNS, or API)
const BASE_DOMAIN = "example.com";
const SUBDOMAINS = ["app", "docs", "api", "staging", "portal", "admin"];

function generateManifestDomains(): string[] {
  return SUBDOMAINS.map(sub => `${sub}.${BASE_DOMAIN}`);
}

// Read the template manifest
const manifest = JSON.parse(fs.readFileSync("manifest.template.json", "utf8"));

// Inject domains into composeExtensions messageHandlers
manifest.composeExtensions[0].messageHandlers[0].value.domains = generateManifestDomains();

// Also inject into validDomains (required for link unfurling)
manifest.validDomains = [
  ...new Set([...(manifest.validDomains ?? []), ...generateManifestDomains()]),
];

fs.writeFileSync("manifest.json", JSON.stringify(manifest, null, 2));
console.log(`Generated manifest with ${SUBDOMAINS.length} domains.`);

Add to your build pipeline: ts-node scripts/generate-manifest-domains.ts before packaging.

Don't: Try to register a single wildcard domain — Teams silently rejects it with no error message.

Reverse (Teams → Slack): Slack supports *.example.com wildcards natively in the app dashboard.

references

• https://learn.microsoft.com/en-us/microsoftteams/platform/messaging-extensions/how-to/link-unfurling

• https://learn.microsoft.com/en-us/microsoftteams/platform/resources/schema/manifest-schema#composeextensionsmessagehandlers

• https://learn.microsoft.com/en-us/microsoftteams/platform/messaging-extensions/what-are-messaging-extensions

• https://github.com/microsoft/teams.ts

• https://api.slack.com/reference/messaging/link-unfurling — Slack link unfurling

• https://api.slack.com/methods/chat.unfurl — Slack chat.unfurl

instructions

Use this expert when adding cross-platform support in either direction for Slack link unfurling or Teams link preview. It covers: link_shared event to message.ext.query-link handler, chat.unfurl() to synchronous card response, manifest messageHandlers domain configuration, the 5-second response deadline, installation requirement, and the lack of retroactive unfurling. For Teams → Slack, map messageHandlers domain config to link_shared event subscription, and preview card responses to chat.unfurl calls. Pair with ../teams/ui.message-extensions-ts.md for general message extension patterns, ../teams/runtime.manifest-ts.md for manifest configuration, and ui-block-kit-adaptive-cards-ts.md for converting between Slack attachment unfurl format and Adaptive Cards.

research

Deep Research prompt:

"Write a micro expert for bridging Slack link unfurling (link_shared event + chat.unfurl) and Teams link preview (compose extension query-link handler, messageHandlers) in either direction for cross-platform bots. Cover: manifest messageHandlers domain configuration, the 5-second synchronous response deadline vs Slack's async model, bot installation requirement, no retroactive unfurling, exact domain matching, Adaptive Card response format, caching strategies, per-URL invocation, and reverse-direction mapping from Teams messageHandlers to Slack link_shared subscriptions and chat.unfurl calls. Include TypeScript code examples and a mapping table."