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

The annotations already declare destructiveHint=true, idempotentHint=true, readOnlyHint=false, and openWorldHint=false, so the safety profile is covered structurally. The description adds the auth requirement ('Requires cost_categories:write scope'), which is genuine value beyond annotations, but it omits patch semantics (does it replace or merge unspecified fields?) and any parent_id/cycle caveats.

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, purpose front-loaded, zero filler. Every clause carries information an agent can act on.

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 an idempotent, non-open-world mutation with a fully-described flat schema and no output schema, the description covers purpose, identity key, and auth scope. The remaining gap is partial-update semantics for optional fields, which is minor given annotations and schema carry the rest.

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% – every parameter (id, name, is_active, parent_id) is documented in the schema with types, formats, and constraints. The description adds nothing about the params beyond 'by ID', so the baseline of 3 applies.

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 ('Update an existing cost category') plus the key discriminator ('by ID'), which cleanly separates it from create_cost_category and delete_cost_category. It does not, however, explicitly name any sibling or contrast with update_work_category/update_part_category for an agent weighing similar update 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?

There is no when-to-use vs when-not guidance, no prerequisite workflow (e.g. 'fetch the id via list_cost_categories first'), and no indication of which alternative tool to pick. Only the auth scope is stated, which is a capability note rather than usage guidance.

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