update_purchase

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

Annotations already declare readOnlyHint=false, idempotentHint=true, destructiveHint=false and openWorldHint=true, so the mutation/safety profile is covered. The description adds real behavioral context beyond that: partial-update semantics ('Only the fields you pass are sent; the rest are left as they are'), accepted date formats, and a feature prerequisite. It stops short of describing failure modes or what the returned object contains, so a 4 rather than 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?

Four short sentences, zero waste, with the verb+resource and mutable field list front-loaded. The alternative-tool routing, partial-update rule, date formats and prerequisite each carry distinct information, so every sentence earns its place.

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?

For a 7-parameter mutation tool with full schema coverage, an output schema (so return values need no explanation) and annotations covering safety, the description supplies everything else an agent needs: partial-update semantics, date formats, sibling routing, and the budget-offer prerequisite.

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 100%, so the baseline is 3, but the description adds meaning the schema does not carry: 'Dates accept YYYY-MM-DD, today or yesterday' gives accepted input formats for paid_at/billed_at that the schema only labels as 'A new paid date'. The partial-update sentence also clarifies that omitted params are intentionally untouched rather than nulled.

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 (Change) and resource (existing purchase) and enumerates the mutable fields, so the scope is unambiguous. It also explicitly names the sibling tools it is not (create_purchase, delete_purchase), letting an agent route without opening other schemas.

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 explicit when-to-use alternatives ('Use create_purchase for a new cost and delete_purchase to remove one') and states a hard precondition ('Requires Gryzzly's budget offer'). Both the selection condition and the eligibility gate are spelled out rather than left to inference.

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