{"version":"2.1.317","anchor":"mcp-tool-errors-use-a-shared-error-classifier","canonical_anchor":"mcp-tool-errors-use-a-shared-error-classifier","heading":"MCP tool error messages are now built by one shared step","tier":"internal","area":"MCP","scope":"individual","heads_up":false,"url":"https:\/\/changelogs.core-directive.com\/v\/2.1.317\/e\/mcp-tool-errors-use-a-shared-error-classifier","release_url":"https:\/\/changelogs.core-directive.com\/v\/2.1.317","markdown":"### MCP tool error messages are now built by one shared step\n\nWhen an MCP tool call fails, Claude Code now works out the error code and message in one shared step instead of building them in place\n\n**Unclear.** It is not clear what wording Claude now sees when an MCP tool call fails.\n\n**What**\n\nMCP servers are outside programs that give Claude Code extra tools. When a call to one of those tools fails, Claude Code works out an error code and a message to describe the failure. That used to happen in place, producing messages such as \"Server answered HTTP\" followed by a status number, or \"Connection error\". Those messages are no longer built here. A shared step now works out the error code, the message and any extra data.\n\n**Why**\n\nThe error text Claude sees when an MCP tool fails may read differently than before.\n\n- Area: MCP\n- Tier: Under the hood\n- Useful: 1\/5\n- Signal: 0\/5\n- Scope: individual\n- Heads-up: no"}