{"version":"2.1.323","anchor":"mcp-tool-call-and-connect-paths-new-reasons-v1compat-telem","canonical_anchor":"mcp-tool-call-and-connect-paths-new-reasons-v1compat-telem","heading":"MCP connections can now fail with \"MCP server held by a hook\"","tier":"notice","area":"MCP","scope":"individual","heads_up":false,"url":"https:\/\/changelogs.core-directive.com\/v\/2.1.323\/e\/mcp-tool-call-and-connect-paths-new-reasons-v1compat-telem","release_url":"https:\/\/changelogs.core-directive.com\/v\/2.1.323","markdown":"### MCP connections can now fail with \"MCP server held by a hook\"\n\nA connection to an MCP server that a hook is holding now fails with the message \"MCP server held by a hook\"\n\n**Unclear.** It is not clear what makes a hook hold an MCP server, or how you would release it.\n\n**What**\n\nMCP servers are outside programs that give Claude Code extra tools. A hook is a command you configure to run at set points while Claude Code works. When a hook is holding an MCP server, a connection attempt to that server now fails with the error \"MCP server held by a hook\".\n\nThere are a few other changes to connecting:\n\n- Failed connection attempts now carry the reason why a server address was not forwarded.\n\n- A successful connection now clears that server from the list of servers whose refresh was refused.\n\n- The usage data recorded for each connection gains a new compatibility field.\n\n**Why**\n\nWhen a connection fails because a hook is holding the server, the error now says so instead of looking like an ordinary connection problem.\n\n- Flag `tengu_mcp_connect_timeout_retry`: Not enough to say (read for one account on one subscription tier against v2.1.323; this account: no value returned, anonymous baseline: no value returned, compiled default: on) These values were read against a different version of Claude Code, so treat them as the nearest reading available instead of one taken on this release.\n- Area: MCP\n- Tier: You'll notice\n- Useful: 2\/5\n- Signal: 2\/5\n- Scope: individual\n- Heads-up: no"}