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

The annotations already declare readOnly/idempotent/non-destructive, so safety is covered; the description adds context above that floor, notably the negative capability ('cannot add funds') and the precise constraints on the add-funds flow (only dashboardUrl, no button, amount, total-after, or steps). It doesn't cover freshness of the balance figure or whether the projection is calendar- or cycle-based, which keeps it off a 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?

The core purpose is front-loaded in the first sentence, and the add-funds routing follows as a distinct clause that earns its place. The final sentence is a dense run-on list of prohibitions that takes a second pass to parse, costing it a perfect score.

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 parameters and no output schema, the description carries the return-value burden and does so by enumerating the four figures returned. Combined with the negative capability and handoff instructions, an agent has enough to invoke it correctly; only staleness/units of the numbers are left implicit.

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. The description correctly implies no inputs are needed by framing it purely around the signed-in user, and it does not waste space inventing parameter guidance.

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 names the specific data returned: signed-in user's balance, this month's spend so far, projected total, and per-hour cost of awake servers. That is a concrete verb+resource statement an agent can act on. It does not, however, distinguish itself from the sibling getMonthSpending, which plausibly covers the same 'this month's spend' data, so the sibling differentiation bar for a 5 isn't met.

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?

It states the trigger explicitly ('when the user asks about their balance or spending'), the exclusion ('it cannot add funds'), and the exact routing for the adjacent intent (show balance plus addFunds with a link to dashboardUrl). This is an unusually complete when/when-not/alternative specification.

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