[BUG] MCP Agent tool reports an empty available-agent list in mcp serve mode

Confirming this in a Docker/Linux setup.

Environment:

• Claude Code: 2.1.90
• OS/runtime: Linux in Docker
• MCP launch path is via docker exec ... claude mcp serve

What we see:

• Inside the same container, normal CLI can see agents via claude agents
• But when Claude Code is started in mcp serve mode, the MCP Agent tool behaves as if the available-agent registry is empty

Repro:

1. Start MCP with:

docker exec -i -w /code/<project> <container> /usr/local/bin/claude mcp serve

1. Initialize MCP normally
2. Call tools/call on Agent with subagent_type: "general-purpose"
3. Result:

Agent type 'general-purpose' not found. Available agents:

Additional data point:

• I also tested starting claude mcp serve with an explicit inline --agents definition
• The MCP Agent call still failed the same way, e.g.:

Agent type 'probe-agent' not found. Available agents:

This suggests the problem is not just discovery of user/global agents from config/home, but that the available-agent list is not being populated at all in mcp serve mode.

Happy to provide the exact JSON-RPC requests/responses if useful.

I'm surprised this is broken.. It seems to have been broken for a while. Any news from Anthropic team here?

I have the same issue.

Still reproduces on Claude Code 2.1.119 (macOS, Darwin 25.4.0). A few extra data points from probing claude mcp serve directly via MCP:

• Cwd doesn't matter. Reproduces identically whether claude mcp serve is launched from $HOME or from a project directory that has its own .claude/agents/.
• Plugin-contributed agents are also missing, not just user ~/.claude/agents/*.md files. I have pr-review-toolkit@claude-plugins-official installed at user scope (visible to the main CLI's Agent tool) and none of its agents show up under mcp serve either. So the scope of the bug is broader than just user-file agents.
• The bug is at tool-registration time, not resolve time. A raw MCP tools/list against claude mcp serve returns the Agent tool with its description already containing an empty Available agent types and the tools they have access to: section (nothing after the colon). So the server literally advertises zero agents — clients aren't just failing to resolve a name, the registry is empty at startup.
• --verbose / --debug flags on claude mcp serve produce no additional info about agent loading beyond the configureGlobalAgents starting / complete pair the original reporter showed.

No workaround found via config. The only way to spawn subagents from inside an MCP-served Claude right now is to shell out to claude -p "..." via the exposed Bash tool, which does load agents normally — but that bypasses the Agent tool entirely and loses streaming/subagent_type/etc.

Any update on this?

Same question, any workarounds for this issue guys? Guys come on, we need to figure something out

Same problem.

Same problem.

Same problem.

Some problem (Claude Code v2.1.133).

We are approaching two months with no formal acknowledgment of this issue. Is anybody (or anything) out there looking at this? It severely limits MCP mode.

We are approaching two months with no formal acknowledgment of this issue. Is anybody (or anything) out there looking at this? It severely limits MCP mode.

Good question. Indeed, this issue is still present in v2.1.146 without any formal acknowledgment.

this issue is still present in 2.1.150

still present in 2.1.181.
Fairly shocking TBH that this gets 0 attention for months!

Still reproduces on Claude Code 2.1.220 on macOS (Darwin arm64).

Normal CLI agent discovery works:

$ claude --agent does-not-exist --model sonnet -p "probe"

--agent 'does-not-exist' not found. Available agents:
claude, codebase-explorer, coder, databricks-analyst, Explore,
general-purpose, jira-scout, observability-analyst, Plan, pr-reviewer,
researcher, slack-scout, statusline-setup, test-runner

The same installation through claude mcp serve has an empty registry:

Agent type 'general-purpose' not found. Available agents:

The same result occurs with a named user agent (coder).

I also tested these server startup variants:

• Explicit --agents definition
• --agent coder
• --setting-sources user,project,local
• CLAUDE_AGENT_SDK_DISABLE_BUILTIN_AGENTS=0
• Combined setting sources, main agent, and built-in-agent flag

Every MCP Agent call still reports an empty available-agent list. The MCP processes have the correct HOME, user, working directory, and readable ~/.claude/agents/*.md files.

Other Claude CLI agent discovery works, so this remains isolated to the mcp serve Agent registry initialization path. No model invocation occurs before the failure.

Reproduced again today (Claude Code MCP registered as a server for Codex, claude mcp serve), but with a different symptom than the empty-registry error above: the Agent tool call failed instantly (~22ms) with user cancelled MCP tool call, not an empty agent list. tool_timeout_sec on the caller side (Codex) was already raised to 600s and made no difference, since nothing waits out a timeout here — the call is rejected before any real work starts.

Setup: codex exec (non-interactive) invoking a claude MCP server entry pointing at claude mcp serve, asking it to call the Agent tool for a general-purpose subagent.

Might be a second failure mode in the same broken registry-init path, or a related permission-gate issue specific to non-interactive/headless MCP clients (no human present to approve a tool call) — flagging in case it's a useful second data point for whoever ends up debugging this.