Single tool with clear naming ('lookup') and good parameter schema. Description is adequate (194 chars, within baseline 34-392 range) but lacks actionable guidance on when/why to use it. Parameter 'mac' has a detailed description with format examples, meeting the 72-char baseline. However, output schema is undocumented, LLMs cannot plan downstream operations or extract structured fields. Error handling returns free-text messages rather than categorized, actionable guidance. No tool annotations (readOnlyHint, idempotentHint). Composition is sound (single responsibility), but lacks pagination/limits documentation and does not return structured metadata useful for chaining.

• Document the output schema explicitly. Define: { mac: string, vendor: string | null, note?: string, error?: string }. Clarify when each field is present.
• Categorize errors with recovery guidance. E.g., { error: 'Rate limited (retryable)', mac, retryAfterSeconds: 1 } or { error: 'Invalid MAC (user-fixable)', mac, hint: 'Provide 6+ hex digits' }.
• Expand tool description to 100-150 chars: 'Look up the hardware manufacturer for a MAC address (OUI). Use when you need to identify network devices. Returns vendor name or null if unregistered. Keyless, free tier ~1 req/sec.'
• Add tool annotations to the schema: { readOnlyHint: true, idempotentHint: true } to signal safe retry behavior.
• Replace example values in parameter description with a regex pattern constraint: 'MAC address or OUI (6+ hex digits). Separators (: - . space) optional. Pattern: ^[0-9a-fA-F:.-\s]+$'