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

Annotations already declare readOnlyHint=true and destructiveHint=false, and the description goes well beyond them: it discloses the enforcement consequence of hitting the limit (hourly servers hibernated with no data loss, prepaid servers unaffected), the specific refused operations and the BUDGET_LIMIT_REACHED error code, plus the billing:read permission and account/MCP-key prerequisites.

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?

Information-dense but the parenthetical clauses and the long enforcement sentence are all load-bearing; the core identity (budget limit, currency, period) is front-loaded. Slightly heavy prose, but very little waste.

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?

With no output schema, the description carries the return-value burden, and it does so explicitly: limit, spend this month/today, percentage used, remaining, and whether the limit was reached. Permission, prerequisites, and enforcement side effects are all covered, so an agent has everything needed.

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?

The tool takes zero parameters, so the baseline is 4 and there is nothing for the description to disambiguate. The description instead fully characterizes the returned values, which is the closest analogue for a no-arg read tool.

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+resource (the account's monthly budget limit and optional daily limit) and pins down currency (CAD) and calendar definition (America/Toronto), which is unusual precision. It is clearly distinguishable from sibling tools like get_balance (money on account) and set_budget (the write counterpart).

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?

The description implies the use case by enumerating what it returns (limit, spend, percentage used, remaining, reached flag), but it never states when to reach for this tool versus get_balance or get_auto_reload, nor does it name any alternative. Usage is left to inference from the content.

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