Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds genuine context beyond that: results come from the most recent completed sync rather than live Xero data, the invoice payload is capped at 50, and email addresses, postal addresses and Xero IDs are deliberately excluded.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Two short sentences with zero filler; the scope and source are front-loaded and the exclusions follow immediately. Every clause carries information an agent needs.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

An output schema exists, so return values need no explanation, and the description covers data freshness, the 50-invoice cap and field exclusions. It stops short of saying whether the cap truncates silently or how a missing or unsynced contact is signalled, which matters for a two-parameter lookup.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 50%: workspace_id is well documented, customer_id has no schema description. The description partially compensates by implying customer_id is an internal customer identifier rather than a Xero ID (which it says are excluded), but it gives no format, provenance, or note on what happens for an unknown customer.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description names a specific verb and resource ('Return one customer contact summary and up to 50 sales invoices') and pins down the data source ('latest completed SHVL Xero sync'). It does not explicitly contrast itself with the sibling search_xero_contacts, though the singular-contact-plus-invoices scope implicitly separates it from the search tools.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Usage is only implied: an agent can infer this is the single-contact lookup keyed by customer_id, as opposed to searching. There is no explicit statement of when to prefer it over search_xero_contacts or get_xero_invoice, and no prerequisites beyond the workspace_id constraint already in the schema.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.