{"version":"2.1.321","anchor":"mcp-file-upload-refusal-and-attach-errors-reworded-names-wi","canonical_anchor":"mcp-file-upload-refusal-and-attach-errors-reworded-names-wi","heading":"Clearer file upload errors for MCP tools, and file names with control characters refused","tier":"notice","area":"MCP","scope":"individual","heads_up":false,"url":"https:\/\/changelogs.core-directive.com\/v\/2.1.321\/e\/mcp-file-upload-refusal-and-attach-errors-reworded-names-wi","release_url":"https:\/\/changelogs.core-directive.com\/v\/2.1.321","markdown":"### Clearer file upload errors for MCP tools, and file names with control characters refused\n\nClaude Code now refuses to attach files whose names contain a line break or other control character, and upload errors are reworded\n\n**What**\n\nMCP servers are add-on programs that give Claude Code extra tools, and some of those tools take files. When Claude Code declines to send a file, its error now says \"Claude Code didn't send any file or run the tool\".\n\nClaude Code now also refuses to attach a file whose name contains a line break or another control character (an invisible character that controls layout rather than showing as text). The error says so. Before, the error mentioned only characters that change the direction of text.\n\n**Why**\n\nThe errors now state plainly that nothing was sent and nothing ran, so you know what happened when an upload is refused.\n\n- Area: MCP\n- Tier: You'll notice\n- Useful: 1\/5\n- Signal: 1\/5\n- Scope: individual\n- Heads-up: no"}