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Emulate slack

Emulated Slack API for local development and testing. Use when the user needs to interact with Slack API endpoints locally, test Slack integrations, emulate channels/messages/users, set up Slack OAuth flows, test incoming webhooks, or work with the Slack Web API without hitting the real Slack API. Triggers include "Slack API", "emulate Slack", "mock Slack", "test Slack OAuth", "Slack bot", "incoming webhook", "local Slack", or any task requiring a local Slack API.

install
source · Clone the upstream repo
git clone https://github.com/vercel-labs/emulate
Claude Code · Install into ~/.claude/skills/
T=$(mktemp -d) && git clone --depth=1 https://github.com/vercel-labs/emulate "$T" && mkdir -p ~/.claude/skills && cp -r "$T/skills/slack" ~/.claude/skills/vercel-labs-emulate-slack && rm -rf "$T"
manifest: skills/slack/SKILL.md
source content

Slack API Emulator

Fully stateful Slack Web API emulation with channels, messages, threads, reactions, OAuth v2, and incoming webhooks. State changes dispatch 

event_callback
payloads to configured webhook URLs.

Start

# Slack only
npx emulate --service slack

# Default port (when run alone)
# http://localhost:4000

Or programmatically:

import { createEmulator } from 'emulate'

const slack = await createEmulator({ service: 'slack', port: 4003 })
// slack.url === 'http://localhost:4003'

Auth

Pass tokens as 

Authorization: Bearer <token>
. All Web API endpoints require authentication.

curl -X POST http://localhost:4003/api/auth.test \
  -H "Authorization: Bearer test_token_admin"

When no token is provided, requests fall back to the first seeded user.

Pointing Your App at the Emulator

Environment Variable

SLACK_EMULATOR_URL=http://localhost:4003

Slack SDK / Bolt

import { WebClient } from '@slack/web-api'

const client = new WebClient(token, {
  slackApiUrl: `${process.env.SLACK_EMULATOR_URL}/api/`,
})

OAuth URL Mapping

Real Slack URLEmulator URL
https://slack.com/oauth/v2/authorize
$SLACK_EMULATOR_URL/oauth/v2/authorize
https://slack.com/api/oauth.v2.access
$SLACK_EMULATOR_URL/api/oauth.v2.access

Auth.js / NextAuth.js

{
  id: 'slack',
  name: 'Slack',
  type: 'oauth',
  authorization: {
    url: `${process.env.SLACK_EMULATOR_URL}/oauth/v2/authorize`,
    params: { scope: 'chat:write,channels:read,users:read' },
  },
  token: {
    url: `${process.env.SLACK_EMULATOR_URL}/api/oauth.v2.access`,
  },
  clientId: process.env.SLACK_CLIENT_ID,
  clientSecret: process.env.SLACK_CLIENT_SECRET,
}

Seed Config

slack:
  team:
    name: My Workspace
    domain: my-workspace
  users:
    - name: developer
      real_name: Developer
      email: dev@example.com
      is_admin: true
    - name: designer
      real_name: Designer
      email: designer@example.com
  channels:
    - name: general
      topic: General discussion
    - name: engineering
      topic: Engineering discussions
      is_private: true
  bots:
    - name: my-bot
  oauth_apps:
    - client_id: "12345.67890"
      client_secret: example_client_secret
      name: My Slack App
      redirect_uris:
        - http://localhost:3000/api/auth/callback/slack
  incoming_webhooks:
    - channel: general
      label: CI Notifications
  signing_secret: my_signing_secret

When no OAuth apps are configured, the emulator accepts any 

client_id
. With apps configured, strict validation is enforced for 
client_id
, 
client_secret
, and 
redirect_uri
.

API Endpoints

Auth

# Test authentication
curl -X POST http://localhost:4003/api/auth.test \
  -H "Authorization: Bearer $TOKEN"

Chat

# Post message
curl -X POST http://localhost:4003/api/chat.postMessage \
  -H "Authorization: Bearer $TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"channel": "C000000001", "text": "Hello from the emulator!"}'

# Post threaded reply
curl -X POST http://localhost:4003/api/chat.postMessage \
  -H "Authorization: Bearer $TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"channel": "C000000001", "text": "Thread reply", "thread_ts": "1234567890.123456"}'

# Update message
curl -X POST http://localhost:4003/api/chat.update \
  -H "Authorization: Bearer $TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"channel": "C000000001", "ts": "1234567890.123456", "text": "Updated message"}'

# Delete message
curl -X POST http://localhost:4003/api/chat.delete \
  -H "Authorization: Bearer $TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"channel": "C000000001", "ts": "1234567890.123456"}'

# /me message
curl -X POST http://localhost:4003/api/chat.meMessage \
  -H "Authorization: Bearer $TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"channel": "C000000001", "text": "is thinking..."}'

Conversations

# List channels (cursor pagination)
curl -X POST http://localhost:4003/api/conversations.list \
  -H "Authorization: Bearer $TOKEN"

# Get channel info
curl -X POST http://localhost:4003/api/conversations.info \
  -H "Authorization: Bearer $TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"channel": "C000000001"}'

# Create channel
curl -X POST http://localhost:4003/api/conversations.create \
  -H "Authorization: Bearer $TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"name": "new-channel", "is_private": false}'

# Channel history (top-level messages only)
curl -X POST http://localhost:4003/api/conversations.history \
  -H "Authorization: Bearer $TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"channel": "C000000001"}'

# Thread replies
curl -X POST http://localhost:4003/api/conversations.replies \
  -H "Authorization: Bearer $TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"channel": "C000000001", "ts": "1234567890.123456"}'

# Join / leave channel
curl -X POST http://localhost:4003/api/conversations.join \
  -H "Authorization: Bearer $TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"channel": "C000000001"}'

# List members
curl -X POST http://localhost:4003/api/conversations.members \
  -H "Authorization: Bearer $TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"channel": "C000000001"}'

Users

# List users (cursor pagination)
curl -X POST http://localhost:4003/api/users.list \
  -H "Authorization: Bearer $TOKEN"

# Get user info
curl -X POST http://localhost:4003/api/users.info \
  -H "Authorization: Bearer $TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"user": "U000000001"}'

# Lookup by email
curl -X POST http://localhost:4003/api/users.lookupByEmail \
  -H "Authorization: Bearer $TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"email": "dev@example.com"}'

Reactions

# Add reaction
curl -X POST http://localhost:4003/api/reactions.add \
  -H "Authorization: Bearer $TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"channel": "C000000001", "timestamp": "1234567890.123456", "name": "thumbsup"}'

# Remove reaction
curl -X POST http://localhost:4003/api/reactions.remove \
  -H "Authorization: Bearer $TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"channel": "C000000001", "timestamp": "1234567890.123456", "name": "thumbsup"}'

# Get reactions
curl -X POST http://localhost:4003/api/reactions.get \
  -H "Authorization: Bearer $TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"channel": "C000000001", "timestamp": "1234567890.123456"}'

Team

# Get workspace info
curl -X POST http://localhost:4003/api/team.info \
  -H "Authorization: Bearer $TOKEN"

Bots

# Get bot info
curl -X POST http://localhost:4003/api/bots.info \
  -H "Authorization: Bearer $TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"bot": "B000000001"}'

Incoming Webhooks

# Post via incoming webhook
curl -X POST http://localhost:4003/services/T000000001/B000000001/X000000001 \
  -H "Content-Type: application/json" \
  -d '{"text": "Deployment complete!"}'

# Post to a specific channel
curl -X POST http://localhost:4003/services/T000000001/B000000001/X000000001 \
  -H "Content-Type: application/json" \
  -d '{"text": "Alert!", "channel": "C000000002"}'

# Post threaded webhook message
curl -X POST http://localhost:4003/services/T000000001/B000000001/X000000001 \
  -H "Content-Type: application/json" \
  -d '{"text": "Thread update", "thread_ts": "1234567890.123456"}'

OAuth

# Authorize (browser flow, shows user picker)
# GET /oauth/v2/authorize?client_id=...&redirect_uri=...&scope=...&state=...

# Token exchange
curl -X POST http://localhost:4003/api/oauth.v2.access \
  -H "Content-Type: application/json" \
  -d '{"client_id": "12345.67890", "client_secret": "example_client_secret", "code": "<code>"}'

Returns a Slack-style response:

{
  "ok": true,
  "access_token": "xoxb-...",
  "token_type": "bot",
  "bot_user_id": "B000000001",
  "team": { "id": "T000000001", "name": "Emulate" },
  "authed_user": { "id": "U000000001" }
}

Event Dispatching

When messages are posted or reactions are added/removed, the emulator dispatches 

event_callback
payloads to configured webhook URLs. These payloads match Slack's Events API format:

  • message
    events on 
    chat.postMessage
    , 
    chat.update
    , 
    chat.delete
  • reaction_added
    / 
    reaction_removed
    events on 
    reactions.add
    / 
    reactions.remove
  • message
    with 
    subtype: bot_message
    on incoming webhook posts

Common Patterns

Post Messages and React

TOKEN="test_token_admin"
BASE="http://localhost:4003"

# Post a message
curl -X POST $BASE/api/chat.postMessage \
  -H "Authorization: Bearer $TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"channel": "C000000001", "text": "Hello!"}'

# React to it (use the ts from the response)
curl -X POST $BASE/api/reactions.add \
  -H "Authorization: Bearer $TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"channel": "C000000001", "timestamp": "<ts>", "name": "wave"}'

OAuth Flow

  1. Redirect user to 
    $SLACK_EMULATOR_URL/oauth/v2/authorize?client_id=...&redirect_uri=...&scope=chat:write,channels:read&state=...
  2. User picks a seeded user on the emulator's UI
  3. Emulator redirects back with 
    ?code=...&state=...
  4. Exchange code for token via 
    POST /api/oauth.v2.access
  5. Use 
    xoxb-
    token to call Web API endpoints

CI Notifications via Webhook

# Use the default incoming webhook
curl -X POST http://localhost:4003/services/T000000001/B000000001/X000000001 \
  -H "Content-Type: application/json" \
  -d '{"text": "Build passed on main"}'