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

Annotations already declare idempotency and non-destructiveness, and the description adds real value beyond them: that amount 0 deletes the plan, that amounts are integers in minor units with a worked example, and the time-zone convention. It does not state error or permission behavior, but this is solid added context.

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?

Front-loaded with the core action and compact. The mention of 'Dates are YYYY-MM-DD' is slightly extraneous since no date parameter exists (only a YYYY-MM period), costing a little precision.

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 write tool with no output schema and no annotation detail, the description covers the mutation's effect, value scaling, and period format adequately. Missing only edge-case/error behavior, which is minor here.

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 0% schema description coverage the description must carry the load, and it does for two of three params: amount units/scale (45000 = 450.00) and the period format/semantics (YYYY-MM budget period). categoryId is left to inference, but its name is self-evident.

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: 'Set a category's planned amount for a budget month.' This clearly distinguishes it from read siblings like get_budget and mutation siblings like copy_budget, though it never names a sibling explicitly.

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?

'amount 0 removes the plan' hints at the two modes of use (planning vs. clearing), but there is no explicit when-to-use guidance or routing to an alternative such as copy_budget for bulk planning. Usage is only implied.

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