Sample — not commissioned

Claude Code dropped one of 19 tools. Renaming two keys got it listed again.

This sample is Claude Code host behaviour. The public package pushpad-mcp@0.1.1 is the reproduction fixture. It is not a defect attributed to the package, and this page does not ask the maintainer to change it.

Host: Claude Code 2.1.282
Fixture: pushpad-mcp@0.1.1
Finding: 1 of 19 tools dropped
Scope: Listing only

What Claude Code did

On the published server, subscriptions_list is the only tool whose input schema has property keys outside /^[a-zA-Z0-9_.-]{1,64}$/. It has two: uids[] and tags[]. Claude Code dropped only that tool. The log named uids[]. The checker stops at the first bad key, so that log does not mention tags[].

Cursor's agent CLI, 2026.09.18-9a7762b, listed all 19 published tools at listing stage only, including both bracketed names. That command prints argument names. It does not send the schema to a model and it does not call the tool.

pushpad-mcp@0.1.1, the same server listed in two hosts

Cursor agent CLI

19 tools listed

14 notification, project and sender tools
subscriptions_create
subscriptions_delete
subscriptions_get
subscriptions_list
subscriptions_update

Claude Code 2.1.282

18 tools listed

14 notification, project and sender tools
subscriptions_create
subscriptions_delete
subscriptions_get
~~subscriptions_list~~ (not listed)
subscriptions_update

Claude Code debug log

Skipping tool "subscriptions_list": its input schema would be rejected by the Anthropic API (property key "uids[]" does not match /^[a-zA-Z0-9_.-]{1,64}$/).

Sample, not commissioned. Listing stage only; no tool was called. Paid packages currently live-check Claude Code; this figure is evidence only.

Runs that isolate the cause

Each row is one Claude Code 2.1.282 tools/list run.

Schema given to Claude Code	Result
Published, with `uids[]` and `tags[]`	Dropped; the log names `uids[]`
Constructed: `uids[]` removed, `tags[]` left	Dropped; the log names `tags[]`
Simplified: `uids[]` renamed to `uids`, `tags[]` left	Dropped for `tags[]`
Smallest: one tool, one property key `tags[]`	No tool listed
Published, with only the two property names renamed	Listed; no `Skipping tool` line

Workaround for a suspected host bug

The published subscriptions_list input schema, with only those two property names changed to uids and tags, was listed. Descriptions, required, outputSchema, and the other 18 tools were unchanged.

uids[]  →  uids
tags[]  →  tags

That result is a listing. It does not show what an invocation would send, and it does not show that a Pushpad query would be correct. The API was not called.

For the host

The runs negotiated MCP 2025-11-25. That specification's Tools section does not set a character pattern on inputSchema property names. The 2026-07-28 Tools page does not add one. The regex is the Anthropic API restriction named in the Claude Code log.

Smallest list that triggers the drop: one tool, one property key tags[]. Claude Code 2.1.282 listed no tool.

Paid live coverage is limited to the host matrix. The tooling behind the checks is Exactlane Preflight.