Why an SDK App With 300 MCP Tools Doesn't Load Them All Upfront
An Agent SDK application connects to an enterprise MCP gateway exposing roughly 300 tools.
By default, how does the SDK handle loading those tool definitions into context?
The correct answer is "Tool search is on by default — only relevant tools load, on demand."
Tool search is on by default in the SDK specifically to avoid paying context-window tokens for hundreds of tool definitions on every turn whether or not they're used. Instead of loading everything upfront, Claude gets a summary of what's available and searches for relevant tools only when a task needs a capability it hasn't already loaded, pulling in up to five of the most relevant matches by default; loaded definitions stay available until compaction clears them.
The distractors describe the opposite or an invented restriction: all 300 definitions don't load upfront by default (that's what tool search exists to avoid); the SDK doesn't reject large catalogs outright (it supports up to 10,000 registered tools); and tools aren't restricted to only what's named explicitly in the prompt — the search mechanism finds them based on the task.
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