Claude Tool Calling Patterns

Tool calls use XML blocks with `<function_calls>` wrapping individual `<invoke>` tags, each containing a `<parameter>` section for arguments. This structure enables Claude to execute tools reliably by marking function names, parameter keys, and values in machine-readable format.

Parallel tool calls execute multiple functions within a single `<function_calls>` block simultaneously. Sequential patterns span multiple blocks across conversation turns, allowing later calls to use results from previous ones—useful when one tool's output feeds into another.

Tool results return structured data back to Claude, typically as JSON within result blocks. Claude expects consistent formatting that maps outputs to the original function call, enabling proper context for follow-up reasoning or chained operations.

Common mistakes include malformed XML tags, missing parameter nesting, inconsistent result formatting, and incorrect parameter type encoding. Debugging relies on validating XML structure, confirming parameter keys match function signatures, and ensuring result data aligns with expected schemas.

Yes, familiarity with XML structure for wrapping calls and JSON for nested parameters is assumed. These formats handle the syntactic layer; understanding both enables you to construct valid invocations and parse tool outputs reliably.

Yes, sequential tool calling spans multiple conversation turns, allowing each request to reference prior results. This multi-turn pattern supports complex workflows where tool outputs inform subsequent function calls or reasoning steps.