Source Intelligence
Follow Discord

DisclaimerUnofficial, and not affiliated with Anthropic. Nearly all of this is read straight out of what ships: npm bundles, captured prompts, published docs. Anthropic's own notes go in verbatim, marked as theirs. The rest is my reading, and every entry carries the strings behind it. If one looks wrong, vote it down and say why.

← All of v2.1.219 Home All releases ←olderv2.1.218 v2.1.220newer→
Claude Code v2.1.219

MCP servers skipped by --mcp-config are now reported

You'll notice
Useful4 Signal0
MCP

MCP servers rejected from --mcp-config are now listed on stderr and in the init message instead of vanishing.

--mcp-configmcp_server_errors
What

Servers passed via --mcp-config that fail validation are no longer silently absent; they are collected, surfaced on the SDK init message, and printed to stderr on a TTY.

Details
  • Validation warnings carrying mcpErrorMetadata.skipReason and a server name are collected, and servers that ended up unregistered are recorded
  • A new optional mcp_server_errors array on the system/init payload lists each skipped entry with name, a stable type category (unknown_type, url_missing_type, invalid_config, reserved_name) and a message, filtered to servers with no live client
  • On a TTY the same list is printed to stderr as a control-character-scrubbed warning
  • Affected servers no longer appear only as gaps in mcp_servers[], so CI can fail on a non-empty list
  • Also new on init: fast_mode_disabled_reason
  • Neither the collection nor the init-message field existed in 2.1.218
Evidence

MCP server config entries from --mcp-config that failed validation and were skipped, skipped due to invalid config

Strings lifted out of the shipped bundle, so the claim above can be checked against them.

Related

Other releases about the same thing. Found by shared names or similar wording; neither means one caused the other.

See this entry in the whole of v2.1.219 →