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

Annotations already carry readOnlyHint=true, so the 'Read-only; nothing is created or changed' sentence is largely redundant. What does add value beyond annotations is the disclosure that accountsReceivableOutstanding/Overdue are raw per-contact figures from Xero (not to be aggregated by the caller) and that `status` is relayed unfiltered, including ARCHIVED, so a listed contact may not be usable. Pagination behaviour and the page cap are left to the schema, keeping it from a 5.

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?

Front-loaded with purpose and read-only status, then the cross-tool disambiguation, then the status caveat. Every sentence carries information, but the final status sentence is long and slightly repetitive of the includeArchived wording; it could be tightened without losing the warning.

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?

With no output schema, the description compensates by naming the key returned fields (accountsReceivableOutstanding/Overdue, status) and their provenance and semantics, and by warning about archived entries. Nothing an agent needs to call this correctly or interpret the response is missing.

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 description coverage is 100%, so the baseline is 3; the description goes beyond it by explaining the practical consequence of `includeArchived` (archived contacts are never filtered out once included, and their `status` must be surfaced) and by defining the `status` vocabulary (ACTIVE/ARCHIVED). It does not clarify the `page` or `organisation` semantics further, which the schema already covers.

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?

States a specific verb and resource ('List contacts ... from Xero') plus scope ('customers and/or suppliers', 'current organisation'), and explicitly routes the aggregation case to get_xero_outstanding_receivables. An agent can distinguish it from create_xero_contact/update_xero_contact and the receivables tool without opening any schema.

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?

Gives an explicit when-not: never sum accountsReceivable* across contacts for 'who owes me the most', use get_xero_outstanding_receivables instead. It also gives an explicit downstream usage rule for `status` (mention it before suggesting a contact be invoiced or updated) and states includeArchived defaults to active-only, so the agent knows the shape of the result set.

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