[BUG] MCP slash commands unrecognized when followed by a prompt

[max-wade-qualia]

Environment

• Platform (select one):
  • [X] Anthropic API
  • [ ] AWS Bedrock
  • [ ] Google Vertex AI
  • [ ] Other:
• Claude CLI version: 1.0.93
• Operating System: macOS 15.6.1
• Terminal: zsh

Bug Description

When I invoke any MCP slash command followed by a prompt, the command isn't recognized.

This works: /zen:chat but this doesn't: /zen:chat foo

The error message I get is Unknown slash command: /zen:chat.

This happens with all of my MCP connections, I have verified the problem does not exist on zen specifically.

Steps to Reproduce

1. Add MCP server of choice to claude
2. Invoke a slash command with a prompt after

Expected Behavior

The command should run, and the string following that slash command should be interpreted as input to that command.

Actual Behavior

I get the error Unknown slash command: /zen:chat

[brandon-reinhart]

All of my commands are giving me unknown slash command today, whether they have text after or not.

[pavelanni]

I am having the same experience as @brandon-reinhart . Also, something has changed in the Claude web client and Claude Desktop, so I can't use MCP server prompts anymore. Just yesterday (2025-08-26), it worked just fine.

[khromov]

There has been a regression, you now cannot use prompts from MCPs any more with Claude Code.

Repro:

1. Add an MCP like this one: claude mcp add --transport http --scope project svelte-llm https://svelte-llm.stanislav.garden/mcp/mcp
2. Search for /svelte-llm and try to add any of the prompts. You get Unknown slash command: svelte-llm:Svelte error, almost like it's not possible to use prompts with spaces.

[DimWebDev]

Me too. I added the same mcp server in VSCode and it works fine. Claude Code lists the slash commands from the mcp server prompts, but when I try to run them, I get “Unknown slash command”.

All of my commands had mandatory and optional arguments based on the typescript mcp sdk docs

[max-wade-qualia]

Anthropic when it’s time to plagiarize from thousands of authors: 🧑‍💻🔥👩‍💻

Anthropic when it’s time to fix basic MCP support (a protocol they invented) in their flagship product: 🥱😴💤

[github-actions[bot]]

This issue has been inactive for 30 days. If the issue is still occurring, please comment to let us know. Otherwise, this issue will be automatically closed in 30 days for housekeeping purposes.

[max-wade-qualia]

Congrats on uhhh donating MCP to the linux foundation but this is still occurring! :(