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

bash

# Slack only
npx emulate --service slack

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

Or programmatically:

typescript

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.

bash

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

bash

SLACK_EMULATOR_URL=http://localhost:4003

Slack SDK / Bolt

typescript

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

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

OAuth URL Mapping

Real Slack URL	Emulator 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

typescript

{
  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

yaml

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

bash

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

Chat

bash

# 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

bash

# 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

bash

# 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

bash

# 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

bash

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

Bots

bash

# 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

bash

# 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

bash

# 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:

json

{
  "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

bash

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

Redirect user to

$SLACK_EMULATOR_URL/oauth/v2/authorize?client_id=...&redirect_uri=...&scope=chat:write,channels:read&state=...

User picks a seeded user on the emulator's UI
Emulator redirects back with
```
?code=...&state=...
```
Exchange code for token via
```
POST /api/oauth.v2.access
```
Use
```
xoxb-
```
token to call Web API endpoints

CI Notifications via Webhook

bash

# 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"}'

slack

NPX Install

Tags

SKILL.md Content

Slack API Emulator

Start

Auth

Pointing Your App at the Emulator

Environment Variable

Slack SDK / Bolt

OAuth URL Mapping

Auth.js / NextAuth.js

Seed Config

API Endpoints

Auth

Chat

Conversations

Users

Reactions

Team

Bots

Incoming Webhooks

OAuth

Event Dispatching

Common Patterns

Post Messages and React

OAuth Flow

CI Notifications via Webhook