Google ADK Skips Page Two of MCP Tool Listings, Hiding Tools From Your Agent
izgorodin · reddit · 2026-11-15
The author diagnosed a real MCP pagination bug: if a tool list spans pages, some clients only fetch page one, making later tools invisible to the model.
Key facts (Google ADK issue #7804)
- A synthetic two-tool stdio server returned alpha on page one and beta on page two; the MCP Python SDK 2.3.0 client could fetch beta when explicitly paging.
- Google ADK 2.13.0's McpToolset.gettools() returned only alpha; server logs show ADK never sent a second tools/list request. No model call involved — purely client-side.
Debugging & pitfalls
- If your agent sees one MCP tool but not another, check server logs for a second tools/list before editing tool descriptions.
- In pagination loops, stop when nextcursor is None: per the MCP spec, an empty string is a valid continuation token, and if not nextcursor wrongly discards it (the SDK still returned beta when echoing the empty token back).
Status
- Source check on Nov 14: ADK 2.14.1 still makes one listing call; fix PR #7805 remains open. Repro done on 2.13.0; write-up AI-assisted.
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