claude-code - 💡(How to fix) Fix [BUG] slack_read_channel / slack_read_thread drop message attachments and blocks [1 participants]

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anthropics/claude-code#51720Fetched 2026-04-22 07:54:38
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Preflight Checklist

  • I have searched existing issues and this hasn't been reported yet
  • This is a single bug report (please file separate reports for different bugs)
  • I am using the latest version of Claude Code

What's Wrong?

The slack_read_channel and slack_read_thread tools only return the top-level text field from Slack messages. Content stored in attachments or Block Kit blocks is silently discarded, causing many messages to appear completely empty even when they have visible content in the Slack UI. Many Slack bots (alerting systems and monitoring tools) store their entire payload in attachments or blocks and set no top-level text field. This makes those messages completely invisible to Claude via the MCP.

What Should Happen?

The tool should surface:

  • attachments[].fallback — the plain-text fallback that well-formed attachments always include
  • attachments[].text and attachments[].fields[].title / .value
  • For Block Kit: plain_text andmrkdwn leaf nodes from the blocks[] tree

Error Messages/Logs

Steps to Reproduce

  1. Connect the claude.ai Slack MCP integration
  2. Find a channel containing bot messages that use attachments or blocks (common for CI bots, alerting systems, monitoring tools, etc.)
  3. Call slack_read_channel — those messages return as empty strings

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Last Working Version

No response

Claude Code Version

2.1.104 (Claude Code)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

No response

extent analysis

TL;DR

The issue can be addressed by modifying the slack_read_channel and slack_read_thread tools to parse and return content from attachments and Block Kit blocks in addition to the top-level text field.

Guidance

  • Review the implementation of slack_read_channel and slack_read_thread to identify where the parsing of Slack message content is happening and modify it to include attachments and Block Kit blocks.
  • Specifically, ensure that the tools are extracting and returning attachments[].fallback, attachments[].text, attachments[].fields[].title, attachments[].fields[].value, and plain-text and mrkdwn leaf nodes from the blocks[] tree.
  • Test the modified tools with a variety of Slack messages that use attachments and blocks to verify that the content is being correctly surfaced.
  • Consider adding logging or debugging statements to help identify any issues that may arise during the parsing process.

Example

No code example is provided as the issue does not include specific implementation details.

Notes

The solution will depend on the specific implementation of the slack_read_channel and slack_read_thread tools, which is not provided in the issue. Additionally, the issue does not specify the programming language or framework being used, which may impact the solution.

Recommendation

Apply a workaround by modifying the slack_read_channel and slack_read_thread tools to parse and return content from attachments and Block Kit blocks, as this will allow the tools to correctly surface content from Slack messages that use these features.

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claude-code - 💡(How to fix) Fix [BUG] slack_read_channel / slack_read_thread drop message attachments and blocks [1 participants]