respond-to-slack-thread

name	respond-to-slack-thread
description	Post a reply to a Slack thread. Use when the user asks to reply to, respond to, or follow up on a Slack thread. Handles fetching thread context and posting a reply.

respond-to-slack-thread

Post a reply to an existing Slack thread. Requires $SLACK_BOT_TOKEN with channels:history, channels:read, and chat:write OAuth scopes.

Step 1: Clarify inputs

Before proceeding, ensure you have:

• Channel ID: The Slack channel ID (e.g. C0123456789). If the user gave a channel name, resolve it in Step 2.
• Thread timestamp (thread_ts): The ts of the parent message (e.g. 1234567890.123456).
  • If the user provided a Slack message link (e.g. https://yourworkspace.slack.com/archives/C0123456789/p1234567890123456), parse it:
    • Channel ID = the segment after /archives/ (e.g. C0123456789)
    • thread_ts = the p-prefixed value at the end, with a decimal inserted 6 characters from the right (e.g. p1234567890123456 → 1234567890.123456)
• Reply content: What to say. If not provided, fetch the thread context (Step 3) and draft a reply based on it.

If $SLACK_BOT_TOKEN is not set, ask the user for it before proceeding.

Step 2: Resolve channel ID (if needed)

If you only have the channel name:

curl -s -H "Authorization: Bearer $SLACK_BOT_TOKEN" \
  "https://slack.com/api/conversations.list?types=public_channel,private_channel&limit=200" | \
  jq -r '.channels[] | select(.name == "<channel_name>") | .id'

If the list is paginated, follow the response_metadata.next_cursor value.

Step 3: Fetch thread context

Read the existing thread to understand the conversation before composing a reply:

curl -s -H "Authorization: Bearer $SLACK_BOT_TOKEN" \
  "https://slack.com/api/conversations.replies?channel=<CHANNEL_ID>&ts=<THREAD_TS>" | \
  jq '.messages[] | {user, ts, text, attachments}'

Review all messages to understand what has already been said before drafting your response.

Step 4: Resolve user info (if needed)

To @mention someone by email:

curl -s -H "Authorization: Bearer $SLACK_BOT_TOKEN" \
  "https://slack.com/api/users.lookupByEmail?email=<email>" | \
  jq -r '.user.id'

Use the resulting ID as <@USER_ID> in the message text.

Step 5: Post the reply

curl -s -X POST \
  -H "Authorization: Bearer $SLACK_BOT_TOKEN" \
  -H "Content-Type: application/json" \
  --data "{
    \"channel\": \"<CHANNEL_ID>\",
    \"thread_ts\": \"<THREAD_TS>\",
    \"text\": \"<MESSAGE_TEXT>\"
  }" \
  "https://slack.com/api/chat.postMessage" | jq '{ok, ts, error}'

For multi-line messages, use $'...' ANSI-C quoting so \n is interpreted as real newlines:

MESSAGE=$'First line\n\nSecond line'
curl -s -X POST \
  -H "Authorization: Bearer $SLACK_BOT_TOKEN" \
  -H "Content-Type: application/json" \
  --data "$(jq -n --arg channel "<CHANNEL_ID>" --arg thread_ts "<THREAD_TS>" --arg text "$MESSAGE" \
    '{channel: $channel, thread_ts: $thread_ts, text: $text}')" \
  "https://slack.com/api/chat.postMessage" | jq '{ok, ts, error}'

Slack mrkdwn formatting

Slack uses its own mrkdwn syntax — do NOT use standard Markdown:

Intent	Slack mrkdwn
@mention user	<@USER_ID>
Hyperlink	<https://example.com|link text>
Bold	*bold*
Italic	_italic_
Strikethrough	~strikethrough~
Code (inline)	`code`
Code block	```code block```

Step 6: Confirm

After posting, share the reply's permalink with the user:

curl -s -H "Authorization: Bearer $SLACK_BOT_TOKEN" \
  "https://slack.com/api/chat.getPermalink?channel=<CHANNEL_ID>&message_ts=<REPLY_TS>" | \
  jq -r '.permalink'

Notes

• If the API returns ok: false, check the error field and handle it — common errors include not_in_channel (bot must be invited to the channel) and missing_scope (token lacks required permissions).
• To post as the bot's configured name/icon rather than a user, ensure the token is a bot token (starts with xoxb-).
• If thread_ts is omitted, the message posts as a new top-level message rather than a reply.