What was spent

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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered. The description adds useful scope context — the two time windows (today and this month) and the notion of a nearest-limit per platform — but says nothing about freshness, caching, or what happens when no usage exists.

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?

It is a single run-on sentence of roughly seventy words with nested parentheticals; the most important content (spend, budget left) is front-loaded correctly, which earns credit. But phrasing like 'the 5 hours before the week' is opaque jargon and the clause chain makes the enumeration hard to parse.

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 and no parameters, the description carries the burden of telling the agent what comes back, and it does enumerate the returned sections thoroughly. Gaps remain in units, format, and undefined domain terms ('Leanfare', 'Auto', 'grades'), which a caller would need to interpret the response.

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 and the schema is fully self-describing, so there is nothing for the description to disambiguate. Baseline 4 applies; the description correctly does not waste words restating an empty schema.

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 enumerates the resource it reports on — today's and this month's spend, budget remaining, Auto savings, top models, plan/delegate work, grades, and per-platform remaining headroom — so an agent can tell it is a spend/usage summary. However, there is no explicit verb, and the sprawl of unrelated facets (grades, platform limits, plans) blurs what the tool's core purpose is versus siblings like report, estimate, or models.

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 statement of when to call this versus alternatives such as estimate (forecasting), report (detailed breakdown), or models (model list). The agent is left to infer that this is the daily 'dashboard' read, and nothing tells it when this tool is the wrong choice.

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