🚨 Slack Error: 'no_text' — Cause, Fix, and Troubleshooting Guide

Overview

no_text means Slack received a chat.postMessage (or chat.update) call with no usable message content — no text, and no blocks/attachments that provide a fallback. Most often it appears when you send only blocks and omit the top-level text.

{
    "ok": false,
    "error": "no_text"
}

Symptoms

• Block Kit messages fail while plain-text messages from the same bot succeed.
• The payload has a populated blocks array but no text key.
• A message built by string concatenation posts fine sometimes and fails when the string ends up empty.

Common Root Causes

1. Blocks without a text fallback

blocks render in-app, but Slack requires a top-level text string as the notification/accessibility fallback. Omitting it can yield no_text.

2. Empty or whitespace-only text

Conditionally built strings that resolve to "" (a filtered-out template variable, a null coalesced to empty) leave the message with nothing to send.

3. All content stripped by validation

Sanitising user input can remove every character, leaving an empty text and no blocks.

How to diagnose

Reproduce the blocks-only case:

curl -s -X POST https://slack.com/api/chat.postMessage \
  -H "Authorization: Bearer $SLACK_BOT_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"channel":"C0123456789","blocks":[{"type":"section","text":{"type":"mrkdwn","text":"Deploy finished"}}]}'

{"ok": false, "error": "no_text"}

Add a text fallback and it succeeds:

curl -s -X POST https://slack.com/api/chat.postMessage \
  -H "Authorization: Bearer $SLACK_BOT_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"channel":"C0123456789","text":"Deploy finished","blocks":[{"type":"section","text":{"type":"mrkdwn","text":"Deploy finished"}}]}'

Fixes

• Always send a top-level text summary alongside blocks. It becomes the push/notification preview and screen-reader text.
• Guard against empty strings: default to a non-empty fallback (text = summary or "(no summary)") before the API call.
• Validate before sending: reject a message where both text is empty and blocks is empty rather than letting Slack reject it.

What to watch out for

• The text fallback should describe the message, not just repeat a header — it is what users see in notifications and on unsupported surfaces.
• Attachments can also satisfy content requirements, but attachments are legacy; prefer text + blocks.
• This is an accessibility win, not just error avoidance: screen readers rely on the text field.

Related

• Slack Error: ‘invalid_blocks’
• Slack Error: ‘msg_too_long’
• Slack Block Kit message design for ops