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

Annotations already mark readOnlyHint=true and the description affirms 'Read-only' without contradiction. It adds substantial behavioral context: a currency caveat (never restate or assume currency matches Invio's), error semantics for 401s (plan lacks Xero Projects or reconnect needed), and a summary of the data covered. This goes well beyond what annotations provide.

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?

The description is longer than average but every sentence carries operational value: ID sourcing, read-only confirmation, field coverage, currency rule, and error interpretation. The lead sentence front-loads the core purpose before the details. No filler or repetition of schema-restated facts.

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?

Given no output schema, the description enumerates the key return fields (task/expense totals, invoiced vs to-be-invoiced, deposits, credit notes) and highlights the currency and error behaviors. Combined with the input schema and annotations, an agent has everything needed to call this correctly and interpret results. The only minor omission is a full response structure, but the detailed field listing makes that unnecessary.

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?

With 50% schema description coverage, the description compensates for the undocumented projectId by defining it as a Xero ProjectID GUID sourced from list_xero_projects and never guessed. The organisation parameter is already explained in the schema, so the description needn't repeat it. Together, both parameters are adequately documented.

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 states a specific verb and resource: full detail on one Xero Projects job, including cost and earned amounts. The phrase 'one Xero Projects job' clearly distinguishes it from list_xero_projects and from get_xero_invoice/quote/credit_note siblings by resource type. Clear and specific.

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?

Provides explicit source guidance for projectId (must come from list_xero_projects, never guessed) and confirms the operation is read-only. It also gives domain-specific error handling for 401s. However, it does not explicitly enumerate alternative tools or when not to use this one, though the resource distinction makes this mostly implicit.

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