{"version":"2.1.299","anchor":"tools-gives-a-specific-error-when-given-an-mcp-tool","canonical_anchor":"tools-gives-a-specific-error-when-given-an-mcp-tool","heading":"Clearer messages when --tools or --disallowed-tools cannot block MCP tools","tier":"notice","area":"CLI","scope":"individual","heads_up":false,"url":"https:\/\/changelogs.core-directive.com\/v\/2.1.299\/e\/tools-gives-a-specific-error-when-given-an-mcp-tool","release_url":"https:\/\/changelogs.core-directive.com\/v\/2.1.299","markdown":"### Clearer messages when `--tools` or `--disallowed-tools` cannot block MCP tools\n\n`--tools` now explains it cannot remove MCP tools, and cloud sessions warn when a `--disallowed-tools` connector wildcard blocks nothing\n\n**Unclear.** Whether this error appears only when starting a cloud session is not confirmed.\n\n**What**\n\n`--tools` and `--disallowed-tools` are flags (options given when starting Claude Code) that limit which tools Claude may use. MCP tools come from MCP servers, outside programs that add extra tools, and claude.ai connectors are MCP tools linked through your claude.ai account. Two messages are new:\n\n- `--tools` and MCP tools: an entry in `--tools` that starts with the MCP prefix is now rejected with an explanation: `--tools` limits built-in tools only, and an MCP tool stays in the session unless `--disallowed-tools` names it. Before, such an entry got a generic rule or name-format message. Names starting with the claude.ai connector prefix are now accepted by `--tools` validation.\n\n- Connector wildcards in cloud sessions: when you launch a cloud session, any `--disallowed-tools` rule with a `*` in a claude.ai connector's name is reported as not applied. The note says such a rule blocks no connector in a cloud session and suggests one rule per connector, such as `mcp__claude_ai_Slack`. Before, these rules were not checked at all. Claude Code also now counts connector-name rules by kind (both names, local name only, wildcard) for its usage statistics.\n\n**Why**\n\nBoth cases used to fail quietly: you could believe a tool was blocked when it was not. Now you are told, and if you rely on wildcard rules to block connectors in cloud sessions, you should switch to one rule per connector.\n\n- Area: CLI\n- Names: `--tools`, `--disallowed-tools`\n- Tier: You'll notice\n- Useful: 2\/5\n- Signal: 1\/5\n- Scope: individual\n- Heads-up: no"}