Slack Bot Builder
Build Slack apps using the Bolt framework across Python, JavaScript, and Java.
Covers Block Kit for rich UIs, interactive components, slash commands,
event handling, OAuth installation flows, and Workflow Builder integration.
Focus on best practices for production-ready Slack apps.
Patterns
Bolt App Foundation Pattern
The Bolt framework is Slack's recommended approach for building apps.
It handles authentication, event routing, request verification, and
HTTP request processing so you can focus on app logic.
Key benefits:
- Event handling in a few lines of code
- Security checks and payload validation built-in
- Organized, consistent patterns
- Works for experiments and production
Available in: Python, JavaScript (Node.js), Java
When to use: Starting any new Slack app,Migrating from legacy Slack APIs,Building production Slack integrations
Python Bolt App
from slack_bolt import App
from slack_bolt.adapter.socket_mode import SocketModeHandler
import os
Initialize with tokens from environment
app = App(
token=os.environ["SLACK_BOT_TOKEN"],
signing_secret=os.environ["SLACK_SIGNING_SECRET"]
)
Handle messages containing "hello"
@app.message("hello")
def handle_hello(message, say):
"""Respond to messages containing 'hello'."""
user = message["user"]
say(f"Hey there <@{user}>!")
Handle slash command
@app.command("/ticket")
def handle_ticket_command(ack, body, client):
"""Handle /ticket slash command."""
# Acknowledge immediately (within 3 seconds)
ack()
# Open a modal for ticket creation
client.views_open(
trigger_id=body["trigger_id"],
view={
"type": "modal",
"callback_id": "ticket_modal",
"title": {"type": "plain_text", "text": "Create Ticket"},
"submit": {"type": "plain_text", "text": "Submit"},
"blocks": [
{
"type": "input",
"block_id": "title_block",
"element": {
"type": "plain_text_input",
"action_id": "title_input"
},
"label": {"type": "plain_text", "text": "Title"}
},
{
"type": "input",
"block_id": "desc_block",
"element": {
"type": "plain_text_input",
"multiline": True,
"action_id": "desc_input"
},
"label": {"type": "plain_text", "text": "Description"}
},
{
"type": "input",
"block_id": "priority_block",
"element": {
"type": "static_select",
"action_id": "priority_select",
"options": [
{"text": {"type": "plain_text", "text": "Low"}, "value": "low"},
{"text": {"type": "plain_text", "text": "Medium"}, "value": "medium"},
{"text": {"type": "plain_text", "text": "High"}, "value": "high"}
]
},
"label": {"type": "plain_text", "text": "Priority"}
}
]
}
)
Handle modal submission
@app.view("ticket_modal")
def handle_ticket_submission(ack, body, client, view):
"""Handle ticket modal submission."""
ack()
# Extract values from the view
values = view["state"]["values"]
title = values["title_block"]["title_input"]["value"]
desc = values["desc_block"]["desc_input"]["value"]
priority = values["priority_block"]["priority_select"]["selected_option"]["value"]
user_id = body["user"]["id"]
# Create ticket in your system
ticket_id = create_ticket(title, desc, priority, user_id)
# Notify user
client.chat_postMessage(
channel=user_id,
text=f"Ticket #{ticket_id} created: {title}"
)
Handle button clicks
@app.action("approve_button")
def handle_approval(ack, body, client):
"""Handle approval button click."""
ack()
# Get context from the action
user = body["user"]["id"]
action_value = body["actions"][0]["value"]
# Update the message to remove interactive elements
# (Best practice: prevent double-clicks)
client.chat_update(
channel=body["channel"]["id"],
ts=body["message"]["ts"],
text=f"Approved by <@{user}>",
blocks=[] # Remove interactive blocks
)
Listen for app_home_opened events
@app.event("app_home_opened")
def update_home_tab(client, event):
"""Update the Home tab when user opens it."""
client.views_publish(
user_id=event["user"],
view={
"type": "home",
"blocks": [
{
"type": "section",
"text": {
"type": "mrkdwn",
"text": "Welcome to the Ticket Bot!"
}
},
{
"type": "actions",
"elements": [
{
"type": "button",
"text": {"type": "plain_text", "text": "Create Ticket"},
"action_id": "create_ticket_button"
}
]
}
]
}
)
Socket Mode for development (no public URL needed)
if name == "main":
handler = SocketModeHandler(app, os.environ["SLACK_APP_TOKEN"])
handler.start()
For production, use HTTP mode with a web server
from flask import Flask, request
from slack_bolt.adapter.flask import SlackRequestHandler
flask_app = Flask(name)
handler = SlackRequestHandler(app)
@flask_app.route("/slack/events", methods=["POST"])
def slack_events():
return handler.handle(request)
Anti_patterns
- Not acknowledging requests within 3 seconds
- Blocking operations in the ack handler
- Hardcoding tokens in source code
- Not using Socket Mode for development
Block Kit UI Pattern
Block Kit is Slack's UI framework for building rich, interactive messages.
Compose messages using blocks (sections, actions, inputs) and elements
(buttons, menus, text inputs).
Limits:
- Up to 50 blocks per message
- Up to 100 blocks in modals/Home tabs
- Block text limited to 3000 characters
Use Block Kit Builder to prototype: https://app.slack.com/block-kit-builder
When to use: Building rich message layouts,Adding interactive components to messages,Creating forms in modals,Building Home tab experiences
from slack_bolt import App
import os
app = App(token=os.environ["SLACK_BOT_TOKEN"])
def build_notification_blocks(incident: dict) -> list:
"""Build Block Kit blocks for incident notification."""
severity_emoji = {
"critical": ":red_circle:",
"high": ":large_orange_circle:",
"medium": ":large_yellow_circle:",
"low": ":white_circle:"
}
return [
# Header
{
"type": "header",
"text": {
"type": "plain_text",
"text": f"{severity_emoji.get(incident['severity'], '')} Incident Alert"
}
},
# Details section
{
"type": "section",
"fields": [
{
"type": "mrkdwn",
"text": f"*Incident:*\n{incident['title']}"
},
{
"type": "mrkdwn",
"text": f"*Severity:*\n{incident['severity'].upper()}"
},
{
"type": "mrkdwn",
"text": f"*Service:*\n{incident['service']}"
},
{
"type": "mrkdwn",
"text": f"*Reported:*\n<!date^{incident['timestamp']}^{date_short} {time}|{incident['timestamp']}>"
}
]
},
# Description
{
"type": "section",
"text": {
"type": "mrkdwn",
"text": f"*Description:*\n{incident['description'][:2000]}"
}
},
# Divider
{"type": "divider"},
# Action buttons
{
"type": "actions",
"block_id": f"incident_actions_{incident['id']}",
"elements": [
{
"type": "button",
"text": {"type": "plain_text", "text": "Acknowledge"},
"style": "primary",
"action_id": "acknowledge_incident",
"value": incident['id']
},
{
"type": "button",
"text": {"type": "plain_text", "text": "Resolve"},
"style": "danger",
"action_id": "resolve_incident",
"value": incident['id'],
"confirm": {
"title": {"type": "plain_text", "text": "Resolve Incident?"},
"text": {"type": "mrkdwn", "text": "Are you sure this incident is resolved?"},
"confirm": {"type": "plain_text", "text": "Yes, Resolve"},
"deny": {"type": "plain_text", "text": "Cancel"}
}
},
{
"type": "button",
"text": {"type": "plain_text", "text": "View Details"},
"action_id": "view_incident",
"value": incident['id'],
"url": f"https://incidents.example.com/{incident['id']}"
}
]
},
# Context footer
{
"type": "context",
"elements": [
{
"type": "mrkdwn",
"text": f"Incident ID: {incident['id']} | <https://runbook.example.com/{incident['service']}|View Runbook>"
}
]
}
]
def send_incident_notification(channel: str, incident: dict):
"""Send incident notification with Block Kit."""
blocks = build_notification_blocks(incident)
app.client.chat_postMessage(
channel=channel,
text=f"Incident: {incident['title']}", # Fallback for notifications
blocks=blocks
)
Handle button actions
@app.action("acknowledge_incident")
def handle_acknowledge(ack, body, client):
"""Handle incident acknowledgment."""
ack()
incident_id = body["actions"][0]["value"]
user = body["user"]["id"]
# Update your system
acknowledge_incident(incident_id, user)
# Update message to show acknowledgment
original_blocks = body["message"]["blocks"]
# Add acknowledgment to context
original_blocks[-1]["elements"].append({
"type": "mrkdwn",
"text": f":white_check_mark: Acknowledged by <@{user}>"
})
# Remove acknowledge button (prevent double-click)
action_block = next(b for b in original_blocks if b.get("block_id", "").startswith("incident_actions"))
action_block["elements"] = [e for e in action_block["elements"] if e["action_id"] != "acknowledge_incident"]
client.chat_update(
channel=body["channel"]["id"],
ts=body["message"]["ts"],
blocks=original_blocks
)
Interactive select menus
def build_user_selector_blocks():
"""Build blocks with user selector."""
return [
{
"type": "section",
"text": {"type": "mrkdwn", "text": "Assign this task:"},
"accessory": {
"type": "users_select",
"action_id": "assign_user",
"placeholder": {"type": "plain_text", "text": "Select assignee"}
}
}
]
Overflow menu for more options
def build_task_blocks(task: dict):
"""Build task blocks with overflow menu."""
return [
{
"type": "section",
"text": {"type": "mrkdwn", "text": f"{task['title']}"},
"accessory": {
"type": "overflow",
"action_id": "task_overflow",
"options": [
{
"text": {"type": "plain_text", "text": "Edit"},
"value": f"edit_{task['id']}"
},
{
"text": {"type": "plain_text", "text": "Delete"},
"value": f"delete_{task['id']}"
},
{
"text": {"type": "plain_text", "text": "Share"},
"value": f"share_{task['id']}"
}
]
}
}
]
Anti_patterns
- Exceeding 50 blocks per message
- Not providing fallback text for accessibility
- Hardcoding action_ids (use dynamic IDs when needed)
- Not handling button clicks idempotently
OAuth Installation Pattern
Enable users to install your app in their workspaces via OAuth 2.0.
Bolt handles most of the OAuth flow, but you need to configure it
and store tokens securely.
Key OAuth concepts:
- Scopes define permissions (request minimum needed)
- Tokens are workspace-specific
- Installation data must be stored persistently
- Users can add scopes later (additive)
70% of users abandon installation when confronted with excessive
permission requests - request only what you need!
When to use: Distributing app to multiple workspaces,Building public Slack apps,Enterprise-grade integrations
from slack_bolt import App
from slack_bolt.oauth.oauth_settings import OAuthSettings
from slack_sdk.oauth.installation_store import FileInstallationStore
from slack_sdk.oauth.state_store import FileOAuthStateStore
import os
For production, use database-backed stores
For example: PostgreSQL, MongoDB, Redis
class DatabaseInstallationStore:
"""Store installation data in your database."""
async def save(self, installation):
"""Save installation when user completes OAuth."""
await db.installations.upsert({
"team_id": installation.team_id,
"enterprise_id": installation.enterprise_id,
"bot_token": encrypt(installation.bot_token),
"bot_user_id": installation.bot_user_id,
"bot_scopes": installation.bot_scopes,
"user_id": installation.user_id,
"installed_at": installation.installed_at
})
async def find_installation(self, *, enterprise_id, team_id, user_id=None, is_enterprise_install=False):
"""Find installation for a workspace."""
record = await db.installations.find_one({
"team_id": team_id,
"enterprise_id": enterprise_id
})
if record:
return Installation(
bot_token=decrypt(record["bot_token"]),
# ... other fields
)
return None
Initialize OAuth-enabled app
app = App(
signing_secret=os.environ["SLACK_SIGNING_SECRET"],
oauth_settings=OAuthSettings(
client_id=os.environ["SLACK_CLIENT_ID"],
client_secret=os.environ["SLACK_CLIENT_SECRET"],
scopes=[
"channels:history",
"channels:read",
"chat:write",
"commands",
"users:read"
],
user_scopes=[], # User token scopes if needed
installation_store=DatabaseInstallationStore(),
state_store=FileOAuthStateStore(expiration_seconds=600)
)
)
OAuth routes are handled automatically by Bolt
/slack/install - Initiates OAuth flow
/slack/oauth_redirect - Handles callback
Flask integration
from flask import Flask, request
from slack_bolt.adapter.flask import SlackRequestHandler
flask_app = Flask(name)
handler = SlackRequestHandler(app)
@flask_app.route("/slack/install", methods=["GET"])
def install():
return handler.handle(request)
@flask_app.route("/slack/oauth_redirect", methods=["GET"])
def oauth_redirect():
return handler.handle(request)
@flask_app.route("/slack/events", methods=["POST"])
def slack_events():
return handler.handle(request)
Handle installation success/failure
@app.oauth_success
def handle_oauth_success(args):
"""Called when OAuth completes successfully."""
installation = args["installation"]
# Send welcome message
app.client.chat_postMessage(
token=installation.bot_token,
channel=installation.user_id,
text="Thanks for installing! Type /help to get started."
)
return "Installation successful! You can close this window."
@app.oauth_failure
def handle_oauth_failure(args):
"""Called when OAuth fails."""
error = args.get("error", "Unknown error")
return f"Installation failed: {error}"
Scope management - request additional scopes when needed
def request_additional_scopes(team_id: str, new_scopes: list):
"""
Generate URL for user to add scopes.
Note: Existing tokens retain old scopes.
User must re-authorize for new scopes.
"""
base_url = "https://slack.com/oauth/v2/authorize"
params = {
"client_id": os.environ["SLACK_CLIENT_ID"],
"scope": ",".join(new_scopes),
"team": team_id
}
return f"{base_url}?{urlencode(params)}"
Anti_patterns
- Requesting unnecessary scopes upfront
- Storing tokens in plain text
- Not validating OAuth state parameter (CSRF risk)
- Assuming tokens have new scopes after config change
Socket Mode Pattern
Socket Mode allows your app to receive events via WebSocket instead
of public HTTP endpoints. Perfect for development and apps behind
firewalls.
Benefits:
- No public URL needed
- Works behind corporate firewalls
- Simpler local development
- Real-time bidirectional communication
Limitation: Not recommended for high-volume production apps.
When to use: Local development,Apps behind corporate firewalls,Internal tools with security constraints,Prototyping and testing
from slack_bolt import App
from slack_bolt.adapter.socket_mode import SocketModeHandler
import os
Socket Mode requires an app-level token (xapp-...)
Create in App Settings > Basic Information > App-Level Tokens
Needs 'connections:write' scope
app = App(token=os.environ["SLACK_BOT_TOKEN"])
@app.message("hello")
def handle_hello(message, say):
say(f"Hey <@{message['user']}>!")
@app.command("/status")
def handle_status(ack, say):
ack()
say("All systems operational!")
@app.event("app_mention")
def handle_mention(event, say):
say(f"You mentioned me, <@{event['user']}>!")
if name == "main":
# SocketModeHandler manages the WebSocket connection
handler = SocketModeHandler(
app,
os.environ["SLACK_APP_TOKEN"] # xapp-... token
)
print("Starting Socket Mode...")
handler.start()
For async apps
from slack_bolt.async_app import AsyncApp
from slack_bolt.adapter.socket_mode.async_handler import AsyncSocketModeHandler
import asyncio
async_app = AsyncApp(token=os.environ["SLACK_BOT_TOKEN"])
@async_app.message("hello")
async def handle_hello_async(message, say):
await say(f"Hey <@{message['user']}>!")
async def main():
handler = AsyncSocketModeHandler(async_app, os.environ["SLACK_APP_TOKEN"])
await handler.start_async()
if name == "main":
asyncio.run(main())
Anti_patterns
- Using Socket Mode for high-volume production apps
- Not handling WebSocket disconnections
- Forgetting to create app-level token
- Using bot token instead of app token
Workflow Builder Step Pattern
Extend Slack's Workflow Builder with custom steps powered by your app.
Users can include your custom steps in their no-code workflows.
Workflow steps can:
- Collect input from users
- Execute custom logic
- Output data for subsequent steps
When to use: Integrating with Workflow Builder,Enabling non-technical users to use your features,Building reusable automation components
from slack_bolt import App
from slack_bolt.workflows.step import WorkflowStep
import os
app = App(
token=os.environ["SLACK_BOT_TOKEN"],
signing_secret=os.environ["SLACK_SIGNING_SECRET"]
)
Define the workflow step
def edit(ack, step, configure):
"""Called when user adds/edits the step in Workflow Builder."""
ack()
# Show configuration modal
blocks = [
{
"type": "input",
"block_id": "ticket_type",
"element": {
"type": "static_select",
"action_id": "type_select",
"options": [
{"text": {"type": "plain_text", "text": "Bug"}, "value": "bug"},
{"text": {"type": "plain_text", "text": "Feature"}, "value": "feature"},
{"text": {"type": "plain_text", "text": "Task"}, "value": "task"}
]
},
"label": {"type": "plain_text", "text": "Ticket Type"}
},
{
"type": "input",
"block_id": "title_input",
"element": {
"type": "plain_text_input",
"action_id": "title"
},
"label": {"type": "plain_text", "text": "Title"}
},
{
"type": "input",
"block_id": "assignee_input",
"element": {
"type": "users_select",
"action_id": "assignee"
},
"label": {"type": "plain_text", "text": "Assignee"}
}
]
configure(blocks=blocks)
def save(ack, view, update):
"""Called when user saves step configuration."""
ack()
values = view["state"]["values"]
# Define inputs (from user's configuration)
inputs = {
"ticket_type": {
"value": values["ticket_type"]["type_select"]["selected_option"]["value"]
},
"title": {
"value": values["title_input"]["title"]["value"]
},
"assignee": {
"value": values["assignee_input"]["assignee"]["selected_user"]
}
}
# Define outputs (available to subsequent steps)
outputs = [
{
"name": "ticket_id",
"type": "text",
"label": "Created Ticket ID"
},
{
"name": "ticket_url",
"type": "text",
"label": "Ticket URL"
}
]
update(inputs=inputs, outputs=outputs)
def execute(step, complete, fail):
"""Called when the step runs in a workflow."""
inputs = step["inputs"]
try:
# Get input values
ticket_type = inputs["ticket_type"]["value"]
title = inputs["title"]["value"]
assignee = inputs["assignee"]["value"]
# Create ticket in your system
ticket = create_ticket(
type=ticket_type,
title=title,
assignee=assignee
)
# Complete with outputs
complete(outputs={
"ticket_id": ticket["id"],
"ticket_url": ticket["url"]
})
except Exception as e:
fail(error={"message": str(e)})
Register the workflow step
create_ticket_step = WorkflowStep(
callback_id="create_ticket_step",
edit=edit,
save=save,
execute=execute
)
app.step(create_ticket_step)
Anti_patterns
- Not calling complete() or fail() in execute
- Long-running operations without progress updates
- Not validating inputs in execute
- Exposing sensitive data in outputs
Sharp Edges
Missing 3-Second Acknowledgment (Timeout)
Severity: CRITICAL
Situation: Handling slash commands, shortcuts, or interactive components
Symptoms:
User sees "This command timed out" or "Something went wrong."
The action never completes even though your code runs.
Works in development but fails in production.
Why this breaks:
Slack requires acknowledgment within 3 seconds for ALL interactive requests:
- Slash commands
- Button/select menu clicks
- Modal submissions
- Shortcuts
If you do ANY slow operation (database, API call, LLM) before responding,
you'll miss the window. Slack shows an error even if your bot eventually
processes the request correctly.
Recommended fix:
Acknowledge immediately, process later
from slack_bolt import App
from slack_bolt.adapter.socket_mode import SocketModeHandler
import threading
app = App(token=os.environ["SLACK_BOT_TOKEN"])
@app.command("/slow-task")
def handle_slow_task(ack, command, client, respond):
ack("Processing your request...")
def do_work():
result = call_slow_api(command["text"])
respond(f"Done! Result: {result}")
threading.Thread(target=do_work).start()
@app.view("modal_submission")
def handle_modal(ack, body, client, view):
ack(response_action="clear")
user_id = body["user"]["id"]
values = view["state"]["values"]
For Bolt framework - use lazy listeners
@app.command("/slow-task")
def handle_slow_task(ack, command, respond):
ack()
@handle_slow_task.lazy
def process_slow_task(command, respond):
result = slow_operation(command["text"])
respond(result)
Not Validating OAuth State Parameter (CSRF)
Severity: CRITICAL
Situation: Implementing OAuth installation flow
Symptoms:
Bot appears to work, but you're vulnerable to CSRF attacks.
Attackers could trick users into installing malicious configurations.
Why this breaks:
The OAuth state parameter prevents CSRF attacks. Flow:
- You generate random state, store it, send to Slack
- User authorizes in Slack
- Slack redirects back with code + state
- You MUST verify state matches what you stored
Without this, an attacker can craft a malicious OAuth URL and trick
admins into completing the flow with attacker's authorization code.
Recommended fix:
Proper state validation
import secrets
from flask import Flask, request, session, redirect
from slack_sdk.oauth import AuthorizeUrlGenerator
from slack_sdk.oauth.state_store import FileOAuthStateStore
app = Flask(__name__)
app.secret_key = os.environ["SESSION_SECRET"]
state_store = FileOAuthStateStore(
expiration_seconds=300,
base_dir="./oauth_states"
)
@app.route("/slack/install")
def install():
state = state_store.issue()
session["oauth_state"] = state
authorize_url = AuthorizeUrlGenerator(
client_id=os.environ["SLACK_CLIENT_ID"],
scopes=["channels:history", "chat:write"],
user_scopes=[]
).generate(state)
return redirect(authorize_url)
@app.route("/slack/oauth/callback")
def oauth_callback():
received_state = request.args.get("state")
stored_state = session.get("oauth_state")
if not received_state or received_state != stored_state:
return "Invalid state parameter - possible CSRF attack", 403
if not state_store.consume(received_state):
,
code = request.args.get()
Exposing Bot/User Tokens
Severity: CRITICAL
Situation: Storing or logging Slack tokens
Symptoms:
Unauthorized messages sent from your bot. Attackers reading private
channels. Token found in logs, git history, or client-side code.
Why this breaks:
Slack tokens provide FULL access to whatever scopes they have:
- Bot tokens (xoxb-*): Access workspaces where installed
- User tokens (xoxp-*): Access as that specific user
- App-level tokens (xapp-*): Socket Mode connections
Common exposure points:
- Hardcoded in source code
- Logged in error messages
- Sent to frontend/client
- Stored in database without encryption
Recommended fix:
Never hardcode or log tokens
client = WebClient(token="xoxb-12345-...")
client = WebClient(token=os.environ["SLACK_BOT_TOKEN"])
logger.error(f"API call failed with token {token}")
logger.error(f"API call failed for team {team_id}")
return {"token": bot_token}
return {"channels": channel_list}
Encrypt tokens in database
from cryptography.fernet import Fernet
class TokenStore:
def __init__(self, encryption_key: str):
self.cipher = Fernet(encryption_key)
def save_token(self, team_id: str, token: str):
encrypted = self.cipher.encrypt(token.encode())
db.execute(
"INSERT INTO installations (team_id, encrypted_token) VALUES (?, ?)",
(team_id, encrypted)
)
def get_token(self, team_id: str) -> str:
row = db.execute(
"SELECT encrypted_token FROM installations WHERE team_id = ?",
(team_id,)
).fetchone()
return self.cipher.decrypt(row[0]).decode()
Rotate tokens if exposed
1. Slack API > Your App > OAuth & Permissions
2. Click "Rotate" for the exposed token
3. Update all deployments immediately
4. Review Slack audit logs for unauthorized access
Requesting Unnecessary OAuth Scopes
Severity: HIGH
Situation: Configuring OAuth scopes for your app
Symptoms:
Users hesitate to install due to scary permission warnings.
Lower install rates. Security team blocks deployment.
App rejected from Slack App Directory.
Why this breaks:
Each OAuth scope grants specific permissions. Requesting more than
you need:
- Makes install consent screen scary
- Increases attack surface if token leaked
- May violate enterprise security policies
- Can get your app rejected from App Directory
Common over-requests:
admin when you just need chat:writechannels:read when you only message one channelusers:read.email when you don't need emails
Recommended fix:
Request minimum required scopes
MINIMAL_SCOPES = [
"chat:write",
"channels:join",
]
SLASH_COMMAND_SCOPES = [
"commands",
"chat:write",
]
MENTION_BOT_SCOPES = [
"app_mentions:read",
"chat:write",
]
Scope reference by use case
| Use Case | Required Scopes |
|---|
| Post messages | chat:write |
| Slash commands | commands |
| Respond to @mentions | app_mentions:read, chat:write |
| Read channel messages | channels:history (public), groups:history (private) |
| Read user info | users:read |
| Open modals | commands or trigger from event |
| Add reactions | reactions:write |
| Upload files | files:write |
Progressive scope requests
INITIAL_SCOPES = ["chat:write", "commands"]
@app.command("/enable-reactions")
def enable_reactions(ack, client, command):
ack()
auth_result = client.auth_test()
if needs_additional_scope:
pass
Exceeding Block Kit Limits
Severity: MEDIUM
Situation: Building complex message UIs with Block Kit
Symptoms:
Message fails to send with "invalid_blocks" error.
Modal won't open. Message truncated unexpectedly.
Why this breaks:
Block Kit has strict limits that aren't always obvious:
- 50 blocks per message/modal
- 3000 characters per text block
- 10 elements per actions block
- 100 options per select menu
- Modal: 50 blocks, 24KB total
- Home tab: 100 blocks
Exceeding these causes silent failures or cryptic errors.
Recommended fix:
Know and respect the limits
BLOCK_KIT_LIMITS = {
"blocks_per_message": 50,
"blocks_per_modal": 50,
"blocks_per_home": 100,
"text_block_chars": 3000,
"elements_per_actions": 10,
"options_per_select": 100,
"modal_total_bytes": 24 * 1024,
}
def validate_blocks(blocks: list) -> tuple[bool, str]:
"""Validate blocks before sending."""
if len(blocks) > BLOCK_KIT_LIMITS["blocks_per_message"]:
return False, f"Too many blocks: {len(blocks)} > 50"
for block in blocks:
if block.get("type") == "section":
text = block.get("text", {}).get("text", "")
if len(text) > BLOCK_KIT_LIMITS["text_block_chars"]:
return False, f"Text too long: {len(text)} > 3000"
if block.get() == :
elements = block.get(, [])
(elements) > BLOCK_KIT_LIMITS[]:
,
,
():
start = page * per_page
end = start + per_page
page_blocks = blocks[start:end]
(blocks) > per_page:
page_blocks.append({
: ,
: [
{: , : {: , : },
: , : page == },
{: , : {: , : },
: ,
: end >= (blocks)}
]
})
page_blocks
Using Socket Mode in Production
Severity: HIGH
Situation: Deploying Slack bot to production
Symptoms:
Bot works in development but is unreliable in production.
Missed events. Connection drops. Can't scale horizontally.
Why this breaks:
Socket Mode is designed for development:
- Single WebSocket connection per app
- Can't scale to multiple instances
- Connection can drop (needs reconnect logic)
- No built-in load balancing
For production with multiple instances or high traffic,
HTTP webhooks are more reliable.
Recommended fix:
Socket Mode: Only for development
if os.environ.get("ENVIRONMENT") == "development":
from slack_bolt.adapter.socket_mode import SocketModeHandler
handler = SocketModeHandler(app, os.environ["SLACK_APP_TOKEN"])
handler.start()
Production: Use HTTP endpoints
from slack_bolt.adapter.flask import SlackRequestHandler
from flask import Flask, request
flask_app = Flask(__name__)
handler = SlackRequestHandler(app)
@flask_app.route("/slack/events", methods=["POST"])
def slack_events():
return handler.handle(request)
@flask_app.route("/slack/commands", methods=["POST"])
def slack_commands():
return handler.handle(request)
@flask_app.route("/slack/interactions", methods=["POST"])
def slack_interactions():
return handler.handle(request)
If you must use Socket Mode in production
from slack_bolt.adapter.socket_mode import SocketModeHandler
import time
class RobustSocketHandler:
def __init__(self, app, app_token):
self.app = app
self.app_token = app_token
self.handler = None
def start(self):
while True:
try:
self.handler = SocketModeHandler(self.app, self.app_token)
self.handler.start()
except Exception as e:
logger.error(f"Socket Mode disconnected: {e}")
time.sleep(5)
Not Verifying Request Signatures
Severity: CRITICAL
Situation: Receiving webhooks from Slack
Symptoms:
Attackers can send fake requests to your webhook endpoints.
Spoofed slash commands. Fake event notifications processed.
Why this breaks:
Slack signs all requests with X-Slack-Signature header using your
signing secret. Without verification, anyone who knows your webhook
URL can send fake requests.
This is different from OAuth tokens - signing verifies the REQUEST
came from Slack, not that you have permission to call Slack.
Recommended fix:
Bolt handles this automatically
from slack_bolt import App
app = App(
token=os.environ["SLACK_BOT_TOKEN"],
signing_secret=os.environ["SLACK_SIGNING_SECRET"]
)
Manual verification (if not using Bolt)
import hmac
import hashlib
import time
from flask import Flask, request, abort
SIGNING_SECRET = os.environ["SLACK_SIGNING_SECRET"]
def verify_slack_signature(request):
timestamp = request.headers.get("X-Slack-Request-Timestamp", "")
signature = request.headers.get("X-Slack-Signature", "")
if abs(time.time() - int(timestamp)) > 60 * 5:
return False
sig_basestring = f"v0:{timestamp}:{request.get_data(as_text=True)}"
expected_sig = "v0=" + hmac.new(
SIGNING_SECRET.encode(),
sig_basestring.encode(),
hashlib.sha256
).hexdigest()
return hmac.compare_digest(expected_sig, signature)
@app.route("/slack/events", methods=["POST"])
def slack_events():
if not verify_slack_signature(request):
abort(403)
Validation Checks
Hardcoded Slack Token
Severity: ERROR
Slack tokens must never be hardcoded
Message: Hardcoded Slack token detected. Use environment variables.
Signing Secret in Source Code
Severity: ERROR
Signing secrets should be in environment variables
Message: Hardcoded signing secret. Use os.environ['SLACK_SIGNING_SECRET'].
Webhook Without Signature Verification
Severity: ERROR
Slack webhooks must verify X-Slack-Signature
Message: Webhook without signature verification. Use Bolt or verify manually.
Slack Token in Client-Side Code
Severity: ERROR
Never expose Slack tokens to browsers
Message: Slack credentials exposed client-side. Only use server-side.
Slow Operation Before Acknowledgment
Severity: WARNING
ack() must be called before slow operations
Message: Slow operation before ack(). Call ack() first, then process.
Missing Acknowledgment Call
Severity: WARNING
Interactive handlers must call ack()
Message: Handler missing ack() call. Must acknowledge within 3 seconds.
OAuth Without State Validation
Severity: ERROR
OAuth callback must validate state parameter
Message: OAuth without state validation. Vulnerable to CSRF attacks.
Token Storage Without Encryption
Severity: WARNING
Tokens should be encrypted at rest
Message: Token stored without encryption. Encrypt tokens at rest.
Requesting Admin Scopes
Severity: WARNING
Avoid admin scopes unless absolutely necessary
Message: Requesting admin scope. Use minimal required scopes.
Potentially Unused Scope
Severity: INFO
Check if all requested scopes are used
Message: Requesting users:read.email but may not use email. Verify necessity.
Collaboration
Delegation Triggers
- user needs AI-powered Slack bot -> llm-architect (Integrate LLM for conversational Slack bot)
- user needs voice notifications -> twilio-communications (Escalate Slack alerts to SMS or voice calls)
- user needs workflow automation -> workflow-automation (Slack as trigger/action in n8n/Temporal workflows)
- user needs bot for Discord too -> discord-bot-architect (Cross-platform bot architecture)
- user needs full auth system -> auth-specialist (OAuth, workspace management, enterprise SSO)
- user needs database for bot data -> postgres-wizard (Store installations, user preferences, message history)
- user needs high availability -> devops (Scale webhooks, monitoring, alerting)
When to Use
- User mentions or implies: slack bot
- User mentions or implies: slack app
- User mentions or implies: bolt framework
- User mentions or implies: block kit
- User mentions or implies: slash command
- User mentions or implies: slack webhook
- User mentions or implies: slack workflow
- User mentions or implies: slack interactive
- User mentions or implies: slack oauth
Limitations
- Use this skill only when the task clearly matches the scope described above.
- Do not treat the output as a substitute for environment-specific validation, testing, or expert review.
- Stop and ask for clarification if required inputs, permissions, safety boundaries, or success criteria are missing.
