Slack MCP concise search formats message timestamps incorrectly

[alingse]

Hi Slack team, thanks for maintaining the official Slack MCP integration.

I realize this repository contains the plugin/configuration for connecting clients to Slack's hosted MCP server rather than the server implementation itself. I'm opening this here because it appears to be the closest public GitHub entry point for https://mcp.slack.com/mcp. If there is a better place to report hosted Slack MCP server issues, please feel free to redirect me.

Summary

The official Slack MCP server appears to format message timestamps incorrectly in concise search results.

Affected tools:

• slack_search_public
• slack_search_public_and_private

When these tools are called with response_format: "concise", the output appends impossible future dates such as 56385707-07-18. For the same search results, response_format: "detailed" returns correct Time and Message_ts values.

Minimal reproduction

Call either affected tool with:

{
  "query": "\"opensandbox\"",
  "limit": 6,
  "sort": "timestamp",
  "sort_dir": "desc",
  "response_format": "concise"
}

Then compare with the same request using:

{
  "query": "\"opensandbox\"",
  "limit": 6,
  "sort": "timestamp",
  "sort_dir": "desc",
  "response_format": "detailed"
}

Observed examples

For the same search results, I observed the following differences:

Message_ts: 1779298899.186649
Detailed:   2026-05-21 01:41:39 CST
Concise:    56385707-07-18

Message_ts: 1779287943.014529
Detailed:   2026-05-20 22:39:03 CST
Concise:    56385360-05-09

Message_ts: 1779263556.980099
Detailed:   2026-05-20 15:52:36 CST
Concise:    56384587-08-05

Message_ts: 1779174431.420859
Detailed:   2026-05-19 15:07:11 CST
Concise:    56381763-04-26

Message_ts: 1779173672.775079
Detailed:   2026-05-19 14:54:32 CST
Concise:    56381739-04-11

Message_ts: 1779090562.914829
Detailed:   2026-05-18 15:49:22 CST
Concise:    56379105-08-18

I also checked the original Slack Web API message ts values directly, and they resolve to the same correct timestamps shown by response_format: "detailed".

Likely cause

Slack message timestamps are represented as seconds.microseconds, for example:

1779298899.186649

The concise renderer appears to multiply that value by 1_000_000 and then format the microsecond-expanded value as Unix seconds.

For example:

1779298899.186649 * 1_000_000 = 1779298899186649

Formatting 1779298899186649 as Unix seconds in CST produces:

56385707-07-18

That exactly matches the invalid date appended by the concise search output.

Expected behavior

response_format: "concise" should either omit the timestamp or format Slack Message_ts using the correct unit, e.g.:

1779298899.186649 => 2026-05-21 01:41:39 CST

or the equivalent local timezone.

Additional context

• Slack support ticket: #6802948
• Related Claude Code discussion: [BUG] Slack MCP slack_search_public returns corrupted timestamps anthropics/claude-code#54074

Please let me know if a different public repository or support channel is preferred for hosted Slack MCP server bugs. I can provide redacted raw MCP request/response samples if useful.

[alingse]

@mwbrooks @srtaalej sorry for the direct ping.

Do you know who owns the hosted Slack MCP server renderer for https://mcp.slack.com/mcp?

This looks like a server-side formatting bug in the concise renderer for slack_search_public / slack_search_public_and_private. I opened Slack support ticket #6802948 as well, but wanted to make sure this GitHub issue reaches the right MCP server owner.

Happy to provide redacted raw MCP request/response samples if useful.

[alingse]

@mwbrooks FYI

concise format ---> 56380855-12-19

{
  "case": "default",
  "tool": "slack_search_public",
  "args": {
    "limit": 20,
    "sort": "timestamp",
    "sort_dir": "desc",
    "query": "\"Zatanna\"",
    "response_format": "concise"
  },
  "result": {
    "meta": null,
    "content": [
      {
        "type": "text",
        "text": "{\"results\":\"# Search Results for: \\\"Zatanna\\\"\\n\\n## Messages (1 results)\\n(1 results)\\n1. #inspiration - XX YYY: <https:\\/\\/www.zatanna.ai\\/> YC 2026 Winter portfolio Zatanna reverse-engineers the network traffic behind any portal and turns it into automation with APIs that execute in seconds\\uff0c\\u628a\\u4efb\\u4f55\\u4e00\\u4e2a\\u7f51\\u6218\\u901a\\u8fc7\\u6d41\\u91cf\\u52ab\\u6301\\u548c\\u9006\\u5411\\u53d8\\u6210\\u53ef\\u4ee5\\u81ea\\u52a8\\u5316\\u7684 API\\uff0c\\u5f88 promising\\uff0c\\u4f46\\u6709\\u70b9\\u9b54\\u6cd5 56380855-12-19\\n\",\"pagination_info\":\"End of results - No more pages available.\\\\n\"}",
        "annotations": null,
        "meta": null
      }
    ],
    "structuredContent": null,
    "isError": false
  }
}

detailed format ---> Time: 2026-05-19 07:09:58 CST\nMessage_ts: 1779145798.192919

{
  "case": "default",
  "tool": "slack_search_public",
  "args": {
    "limit": 20,
    "sort": "timestamp",
    "sort_dir": "desc",
    "query": "\"Zatanna\"",
    "response_format": "detailed"
  },
  "result": {
    "meta": null,
    "content": [
      {
        "type": "text",
        "text": "{\"results\":\"# Search Results for: \\\"Zatanna\\\"\\n\\n## Messages (1 results)\\n### Result 1 of 1\\nChannel: #inspiration (ID: C0A37E94PHD)\\nFrom: XX YYY (ID: U0B0E16M3TJ) \\nTime: 2026-05-19 07:09:58 CST\\nMessage_ts: 1779145798.192919\\nPermalink: [link](https:\\/\\/xx-yy.slack.com\\/archives\\/C0A37E94PHD\\/p1779145798192919)\\nText: \\n<https:\\/\\/www.zatanna.ai\\/> YC 2026 Winter portfolio Zatanna reverse-engineers the network traffic behind any portal and turns it into automation with APIs that execute in seconds\\uff0c\\u628a\\u4efb\\u4f55\\u4e00\\u4e2a\\u7f51\\u6218\\u901a\\u8fc7\\u6d41\\u91cf\\u52ab\\u6301\\u548c\\u9006\\u5411\\u53d8\\u6210\\u53ef\\u4ee5\\u81ea\\u52a8\\u5316\\u7684 API\\uff0c\\u5f88 promising\\uff0c\\u4f46\\u6709\\u70b9\\u9b54\\u6cd5\\nContext before: \\n- From: XX YYY (ID: U0B0E16M3TJ) \\n  Message_ts: 1779143963.684159\\n  <https:\\/\\/browse.sh\\/> \\u8ddf\\u4e0a\\u9762\\u7684 opencli \\u5f88\\u50cf\\u7684\\u4ea7\\u54c1\\uff0c\\u66f4\\u52a0\\u9762\\u5411\\u6d77\\u5916\\n```$ browse skills add alltrails.com\\n$ browse skills add recreation.gov\\n$ browse skills add weather.gov\\n$ browse skills add plugshare.com\\n$ browse skills add ramp.com\\n\\n$ claude \\\"Plan a road trip to Utah with EV charging stops and campsites for each night. Book and reimburse on Ramp.\\\"```\\n- From: XX YYY (ID: U0B0E16M3TJ) \\n  Message_ts: 1779145121.680519\\n  <https:\\/\\/polymathlabs.ai\\/blog\\/horizon-swe> YC 2026 Winter portfolio\\uff0c\\u8ddf\\u6211\\u4eec\\u8ba8\\u8bba\\u8fc7\\u7684 e2e eval \\u5f88\\u6709\\u5173\\uff0c\\u4e3a\\u4e86\\u63d0\\u5347\\u81ea\\u4e3b\\u667a\\u80fd\\u4f53\\u7684\\u6027\\u80fd\\uff0c\\u5fc5\\u987b\\u5728\\u80fd\\u591f\\u53cd\\u6620\\u771f\\u5b9e\\u4e16\\u754c\\u7684\\u6a21\\u62df\\u73af\\u5883\\u4e2d\\u5bf9\\u5176\\u8fdb\\u884c\\u8bad\\u7ec3\\u3002Polymath \\u4e3a\\u667a\\u80fd\\u4f53\\u6784\\u5efa\\u6a21\\u62df\\u4e16\\u754c\\uff0c \\u4f9b\\u5176\\u7ec3\\u4e60\\u5e76\\u901a\\u8fc7\\u7ecf\\u9a8c\\u5b66\\u4e60\\u3002\\u7b2c\\u4e00\\u4e2a\\u5de5\\u4f5c\\u662f Horizon SWE bench\\uff0c\\u4e13\\u95e8\\u9020\\u4e86\\u4e00\\u4e2a\\u865a\\u5047\\u7684\\u8f6f\\u4ef6\\u516c\\u53f8\\u53bb\\u8bc4\\u4f30 coding agent\\uff1a\\u6211\\u4eec\\u5c06\\u4e00\\u5bb6\\u5b8c\\u6574\\u7684\\u8f6f\\u4ef6\\u5de5\\u7a0b\\u516c\\u53f8\\u90e8\\u7f72\\u5728\\u4e00\\u4e2a\\u5bb9\\u5668\\u5316\\u73af\\u5883\\u4e2d\\uff0c\\u8be5\\u73af\\u5883\\u5305\\u542b\\u4e00\\u4e2a\\u8fd0\\u884c\\u4e2d\\u7684\\u5e94\\u7528\\u7a0b\\u5e8f\\uff08\\u5e26\\u6709\\u5b9e\\u65f6\\u6d41\\u91cf\\uff09\\u4ee5\\u53ca\\u4e00\\u5957\\u5305\\u542b 73 \\u79cd\\u8f6f\\u4ef6\\u5de5\\u7a0b\\u5de5\\u5177\\u7684\\u5de5\\u5177\\u5305\\u3002\\u7136\\u540e\\uff0c\\u6211\\u4eec\\u8ba9 AI \\u4ee3\\u7406\\u5b8c\\u6210\\u5927\\u578b\\u7684\\u591a\\u6b65\\u9aa4\\u4efb\\u52a1\\uff1a\\u6536\\u96c6\\u4fe1\\u606f\\u3001\\u5b9e\\u73b0\\u529f\\u80fd\\u3001\\u6d4b\\u8bd5\\u3001\\u90e8\\u7f72\\u3001\\u76d1\\u63a7\\u670d\\u52a1\\u4ee5\\u53ca\\u54cd\\u5e94\\u4e8b\\u4ef6\\u3002\\u6700\\u540e\\uff0c\\u6211\\u4eec\\u4ece\\u529f\\u80fd\\u6b63\\u786e\\u6027\\u3001\\u90e8\\u7f72\\u548c\\u8fd0\\u7ef4\\u4ee5\\u53ca\\u5de5\\u7a0b\\u8d28\\u91cf\\u4e09\\u4e2a\\u65b9\\u9762\\u8bc4\\u4f30\\u4e86\\u4ee3\\u7406\\u7684\\u6027\\u80fd\\u3002\\n- From: XX YYY (ID: U0B0E16M3TJ) \\n  Message_ts: 1779145400.569279\\n  <https:\\/\\/heypocket.com\\/pages\\/now> YC 2026 Winter portfolio \\u7f8e\\u56fd\\u7248\\u7684\\u53c8\\u4e00\\u4e2a\\u5f55\\u97f3\\u8c46\\n\\n  - \\u4e00\\u952e\\u5f55\\u97f3\\uff0c\\u652f\\u6301\\u79bb\\u7ebf\\u5f55\\u97f3\\n  - \\u5f55\\u9762\\u5bf9\\u9762\\u8c08\\u8bdd\\u548c\\u7535\\u8bdd\\u901a\\u8bdd\\n  - 64GB \\u672c\\u5730\\u5b58\\u50a8\\n  - 3 \\u4e2a\\u9ea6\\u514b\\u98ce\\uff0c\\u5f55\\u97f3\\u8ddd\\u79bb\\u6807\\u79f0\\u7ea6 15 \\u7c73\\n  - \\u540c\\u6b65\\u5230 App \\u540e\\u81ea\\u52a8\\u8f6c\\u6587\\u5b57\\u3001\\u603b\\u7ed3\\u3001\\u751f\\u6210\\u5f85\\u529e\\/\\u601d\\u7ef4\\u5bfc\\u56fe\\n  - \\u652f\\u6301 iOS\\u3001Android \\u548c\\u7f51\\u9875\\u7aef\\n  - \\u76ee\\u524d\\u9875\\u9762\\u4ef7\\u683c\\u663e\\u793a\\u7ea6 *$129*\\uff0c\\u53e6\\u6709 Pro \\u8ba2\\u9605 *$19.99\\/\\u6708*\\n\\n  \\u6240\\u4ee5\\u5b83\\u4e0d\\u662f\\u5355\\u7eaf\\u5f55\\u97f3\\u7b14\\uff0c\\u66f4\\u50cf Plaud \\/ Limitless Pendant \\u8fd9\\u7c7b AI \\u5f55\\u97f3\\u786c\\u4ef6\\uff1a\\u786c\\u4ef6\\u8d1f\\u8d23\\u6536\\u97f3\\uff0c\\u8f6f\\u4ef6\\u8d1f\\u8d23\\u8f6c\\u5199\\u548c\\u603b\\u7ed3\\u3002\\n\\n---\\n\\n\",\"pagination_info\":\"End of results - No more pages available.\\\\n\"}",
        "annotations": null,
        "meta": null
      }
    ],
    "structuredContent": null,
    "isError": false
  }
}

[alingse]

@stevengill we need help. If you have any time to see this issue that related the slack mcp server side?

[mwbrooks]

Hi @alingse 👋🏻

Wow, absolutely incredible research in narrowing down the issue and discovering the likely cause! 🕵🏻 🏆

You've taken all of the right steps:

1. Submitted a Slack Support Ticket
2. Opened an issue here

You're right that this repo only contains the plugin configuration, but I'm able to share your issue directly with the MCP team. They have a channel where their product manager and engineering team track all internal and external issues.

So, I've submitted this GitHub Issue to the team and I've also linked this GitHub issue and the internal issue to your support ticket. After submitted, our automated systems were able to confirm the bug and notified our PM. So, let's hope the issue is resolved soon!

I'll leave this issue open for a few days and respond with any activity that I see. However, I'll need to close the issue after a while.

Our Support Team is very good and they typically notify you when the issue has been resolved :)

[mwbrooks]

@alingse - Just wanted to let you know that I'm still keeping an eye on this issue - no updates to share yet.