Tool functions returning raw lists produce multiple TextContent blocks, breaking most MCP clients

[EODWeber]

Problem

Several tool functions return raw Python lists (e.g., return events[:limit]). When FastMCP serializes these, each list element becomes a separate TextContent block in the MCP CallToolResult.content array. Most MCP clients — including mcporter, Claude Code via mcp-remote, and others — only read content[0], so they see a single result instead of the full list.

Functions returning Response objects (like ListCalendarsResponse, ListTodosResponse) are unaffected since they serialize as a single JSON object.

Affected Functions

File	Function	Line(s)	Returns
server/calendar.py	nc_calendar_list_events	207, 221	events[:limit] / events
server/calendar.py	nc_calendar_get_upcoming_events	455	all_events[:limit]
server/deck.py	deck_get_boards	131	list[DeckBoard]
server/deck.py	deck_get_stacks	155	list[DeckStack]
server/deck.py	deck_get_cards	182	list[DeckCard]
server/deck.py	deck_get_labels	209	list[DeckLabel]
server/contacts.py	nc_contacts_list_addressbooks	24	list
server/contacts.py	nc_contacts_list_contacts	35	list
server/tables.py	nc_tables_list_tables	24	list

Reproduction

# Returns only 1 event instead of ~20
mcporter call "nextcloud.nc_calendar_list_events(calendar_name: \"outlookoffice365com\", start_date: \"2026-02-18\", end_date: \"2026-02-20\", limit: 100)"

The same query via Anthropic's Cowork MCP client (which reads all content blocks) returns the full result set, confirming the server produces the data correctly but the response serialization causes client-side truncation.

Suggested Fix

Wrap raw list returns in json.dumps() so the entire result serializes as a single TextContent block:

import json

# Before (creates N TextContent blocks):
return events[:limit]

# After (creates 1 TextContent block containing a JSON array):
return json.dumps(events[:limit], default=str)

Alternatively, wrap these returns in Response objects (consistent with how ListCalendarsResponse, ListTodosResponse, etc. already work) to keep a uniform return pattern across the codebase.

Environment

• nextcloud-mcp-server: latest Docker image
• Transport: mcp-remote --transport http-only
• Clients affected: mcporter 0.7.3, Claude Code (via mcp-remote)
• Clients unaffected: Anthropic Cowork (native MCP connector)

[cbcoutinho]

Hi @EODWeber im curious if this is a regression in the MCP SDK - can you confirm of the issue exists in v0.64.0 as well?

I recently bumped the MCP library in v0.64.1 and may not have tested it thoroughly enough.

[cbcoutinho]

I took another look at this issue today, and you are correct. There is inconsistent response handling for tools across apps here - I will consolidate all tool results using the Response object pattern used in most parts of the code base. Thanks for raising the issue, I'll have a PR ready in a bit

[cbcoutinho]

Hi @EODWeber this should now be fixed in v0.64.3 - could you please verify and check that collections are now correctly wrapped for the MCP tool responses you listed above? Feel free to close the issue if this is fixed