Codex does not follow MCP `tools/list` pagination via `nextCursor`

Here is the minimal repro server I used.

Save this as /tmp/mcp_pagination_probe.py:

#!/usr/bin/env python3
import json
import sys


def send(obj):
    sys.stdout.write(json.dumps(obj, separators=(",", ":")) + "\n")
    sys.stdout.flush()


def tool(name):
    return {
        "name": name,
        "description": f"Probe tool {name}",
        "inputSchema": {
            "type": "object",
            "properties": {},
            "additionalProperties": False,
        },
    }


PAGE1 = [tool(f"page1_tool_{i:02d}") for i in range(1, 31)]
PAGE2 = [tool("github-mcp-server___search_repositories")]


for line in sys.stdin:
    line = line.strip()
    if not line:
        continue

    req = json.loads(line)
    print(
        json.dumps(
            {
                "received": {
                    "method": req.get("method"),
                    "id": req.get("id"),
                    "params": req.get("params"),
                }
            }
        ),
        file=sys.stderr,
        flush=True,
    )

    method = req.get("method")
    req_id = req.get("id")

    if method == "initialize":
        send(
            {
                "jsonrpc": "2.0",
                "id": req_id,
                "result": {
                    "protocolVersion": "2025-06-18",
                    "capabilities": {"tools": {}},
                    "serverInfo": {"name": "pagination-probe", "version": "0.1.0"},
                },
            }
        )
    elif method == "notifications/initialized":
        continue
    elif method == "tools/list":
        cursor = (req.get("params") or {}).get("cursor")
        if cursor is None:
            send(
                {
                    "jsonrpc": "2.0",
                    "id": req_id,
                    "result": {"tools": PAGE1, "nextCursor": "page-2"},
                }
            )
        elif cursor == "page-2":
            send(
                {
                    "jsonrpc": "2.0",
                    "id": req_id,
                    "result": {"tools": PAGE2},
                }
            )
        else:
            send(
                {
                    "jsonrpc": "2.0",
                    "id": req_id,
                    "error": {"code": -32602, "message": f"invalid cursor: {cursor}"},
                }
            )
    elif method == "tools/call":
        name = (req.get("params") or {}).get("name")
        send(
            {
                "jsonrpc": "2.0",
                "id": req_id,
                "result": {
                    "content": [{"type": "text", "text": f"called {name}"}],
                    "isError": False,
                },
            }
        )
    elif req_id is not None:
        send(
            {
                "jsonrpc": "2.0",
                "id": req_id,
                "error": {"code": -32601, "message": f"method not found: {method}"},
            }
        )

Then run:

codex exec --json --ignore-user-config --sandbox read-only \
  -c 'mcp_servers.probe={command="python3",args=["/tmp/mcp_pagination_probe.py"],startup_timeout_sec=10,default_tools_approval_mode="approve"}' \
  '
Use only the MCP server named probe.
Do not use shell commands.
First report how many callable tools are available from probe.
Then call github-mcp-server___search_repositories if it is available.
Return OK only if that page-2 tool call succeeds. Otherwise return FAIL with the exact reason.
'

Observed result:

probe exposes 30 callable tools.

FAIL:
github-mcp-server___search_repositories is not available
only mcp__probe.page1_tool_* tools were callable

The server logs show Codex sends only the first tools/list request:

{"method":"initialize","id":0}
{"method":"tools/list","id":1,"params":{"_meta":{"progressToken":0}}}

It never sends a second tools/list request with:

{"cursor":"page-2"}

So the reproduction does not depend on a specific gateway or a specific page size limit. It only depends on a valid paginated tools/list response with nextCursor.

Independent real-world reproduction using an HTTP MCP server built with Laravel MCP v0.5.9:

• The server registers 23 tools.
• The initial authenticated tools/list response returns exactly 15 tools and a nextCursor.
• Codex exposes only those first 15 tools.
• Requesting tools/list again with the returned cursor provides the remaining eight tools.
• Cursor discovers the second-page tools against the same server.

Laravel MCP defaults the page size to 15:

https://github.com/laravel/mcp/blob/39e8da60eb7bce4737c5d868d35a3fe78938c129/src/Server.php#L102-L104

Its tools/list implementation applies cursor pagination here:

https://github.com/laravel/mcp/blob/39e8da60eb7bce4737c5d868d35a3fe78938c129/src/Server/Methods/ListTools.php#L15-L21

Increasing the server’s defaultPaginationLength to 50 works as a compatibility workaround, but Codex should follow nextCursor so paginated MCP servers work without client-specific configuration.

Root cause, minimal repro, and reference fix

Root cause. list_tools_for_client_uncached in codex-rs/codex-mcp/src/rmcp_client.rs issues a single list_tools_with_connector_ids(/*params*/ None, timeout) call and drops the next_cursor field of the response. The lower-level client already surfaces the cursor (ListToolsWithConnectorIdResult.next_cursor in codex-rs/rmcp-client/src/rmcp_client.rs), and Codex already follows cursors for resources/list and resources/templates/list (see the pagination loops in codex-mcp/src/connection_manager.rs, incl. a duplicate-cursor guard). tools/list is the only list endpoint missing that loop.

Real-world repro. codebase-memory-mcp 0.9.0 (stdio) exposes 14 tools, paginated 8 per page:

printf '%s\n' \
'{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2024-11-05","capabilities":{},"clientInfo":{"name":"probe","version":"1.0"}}}' \
'{"jsonrpc":"2.0","method":"notifications/initialized"}' \
'{"jsonrpc":"2.0","id":2,"method":"tools/list","params":{}}' \
'{"jsonrpc":"2.0","id":3,"method":"tools/list","params":{"cursor":"8"}}' \
| codebase-memory-mcp 2>/dev/null \
| jq -c 'select(.id>=2) | {id, count:(.result.tools|length), nextCursor:.result.nextCursor}'

Output:

{"id":2,"count":8,"nextCursor":"8"}
{"id":3,"count":6,"nextCursor":null}

Codex registers only the first 8 tools from this server. As a cross-client control, the same server binary registers all 14 tools in an MCP client that follows nextCursor (Claude Code), so the server side is spec-compliant.

Reference implementation. I applied the same loop pattern Codex already uses for resources (accumulate pages until next_cursor is None, bail on a repeated cursor) to list_tools_for_client_uncached: https://github.com/erictheng93/codex/commit/a27af5f52c280a09ec4dee23b5cf5d465e65c031. cargo check -p codex-mcp passes. Happy to open a PR with test coverage if the team would like to invite one per the contributing policy.