Four well-defined tools with clear, domain-specific descriptions (avg 156 chars). All tools have explicit input schemas with typed parameters and descriptions. Naming follows verb_noun pattern (workbook_overview, list_formulas, trace_cell, audit_workbook). Error handling via guarded() wrapper catches exceptions and returns isError flag. However, output schemas are not formally documented, responses are JSON-stringified but structure is implicit. Parameters lack enums and some constraints (e.g., cell address format). No tool annotations (readOnlyHint). Missing pagination guidance for list_formulas despite accepting limit parameter.

• Document output schemas explicitly. For each tool, define the structure of the returned JSON (e.g., workbook_overview returns {sheets: [{name, dimension, cells, formulas, mergedRanges}], definedNames, externalWorkbookLinks}).
• Add readOnlyHint: true to all four tool inputSchemas to signal read-only safety and enable agent optimizations.
• Add regex pattern constraint to trace_cell's 'cell' parameter: z.string().regex(/^([A-Z]+\d+|'?[^'!]+!'?[A-Z]+\d+)$/).describe('Cell address, e.g. B14 or Summary!B14').
• Implement pagination for list_formulas: add offset/limit or cursor-based continuation. Return {totalMatches, offset, limit, results, hasMore} to enable multi-page queries.
• Enhance error handling: wrap exceptions with context (e.g., 'Failed to load workbook at {path}: {error}. Verify the file exists and is a valid .xlsx file.') and categorize as retryable or user-fixable.