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

Well beyond what readOnlyHint/openWorldHint already declare: it warns that currency and amounts are authoritative as Xero stored them and must never be restated or converted, and it clarifies that a SENT status does not prove delivery. Both are non-obvious behavioral caveats an agent could not infer from annotations or schema.

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?

Three sentences, each carrying distinct payload: purpose/contents first, then the ID constraint, then data-fidelity and status caveats. No filler and the primary purpose is front-loaded.

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 still tells the agent what comes back (line items, title, summary, terms) and how to interpret amounts and status. Nothing an agent needs to call this correctly and interpret the result 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?

The schema documents only 50% of parameters (organisation has a description; quoteId has format/pattern but no prose). The description compensates by explaining what quoteId actually is and where to obtain it, which is the more important half. The organisation parameter is left entirely to the schema.

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?

Opens with a specific verb+resource+scope: "Full detail on one Xero quote", and enumerates what detail means (line items, title, summary, terms). This cleanly separates it from list_xero_quotes and the many get_xero_* siblings that target different resources.

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?

The ID provenance rule ("must be a Xero QuoteID (a GUID) from list_xero_quotes, never an Invio id") effectively routes the agent to the listing tool first and blocks a common wrong-ID failure. It gives clear use context but no explicit when-not-to-use case, so it stops short of a 5.

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