Under the hood
MCP tool permission checks now consult an SDK-registered checker before the usual permission logic
What
When deciding whether an MCP tool (a tool provided by an external MCP server) is allowed to run, Claude Code now first asks a permission checker registered by the SDK (software development kit), if one is present. Only if that doesn't produce a decision does it fall back to the built-in permission-rule logic and design-consent checks it used before.
Why
This lets code built on the Claude Code SDK plug in its own custom permission logic for MCP tools, taking priority over the default rules.