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

Annotations already declare destructiveHint=true, idempotentHint=true, and readOnlyHint=false, so safety profile is covered. The description adds a genuinely useful auth prerequisite ('Requires cost_categories:write scope') that annotations cannot express, but says nothing about partial vs. full replacement semantics or what the destructive flag implies.

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, zero filler, with the core action front-loaded ahead of the permission requirement. Every word 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 mutation tool with a fully documented schema and annotations covering safety, this is minimally adequate. It omits update semantics (partial vs. replace), which fields are optional, and any side effects like deactivation of child categories, leaving an agent to infer too much.

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 all four parameters (id, name, is_active, parent_id) are documented in the schema. The description only restates that lookup is by ID and adds no format or constraint detail beyond the schema, so the baseline 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?

Specific verb+resource: 'Update an existing cost category by ID' clearly states the operation and the identifier required. It doesn't explicitly differentiate from sibling update_* tools or reference create_cost_category/delete_cost_category, but the resource is unambiguous.

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 guidance, no exclusion of edge cases, and no mention of alternatives like create_cost_category or list_cost_categories. The scope sentence speaks to permissions, not usage context.

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