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

With no annotations, the description carries the full behavioral burden and does so well: read-only, live, does not count against quota, only successful calls are counted, and at the limit calls are refused rather than billed as overage. These are exactly the traits an agent needs to reason about cost and rate-limit safety.

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 purpose and usage, then behavior, then return shape. It is dense and somewhat long, but each sentence adds distinct information, and the return-value detail is warranted given there is no output schema.

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?

Without an output schema the description must describe the response, and it does: plan and planLabel, callsUsed, monthlyCalls, callsRemaining with the null-when-uncapped rule, and rateLimit as perSecond/perMinute with the note that a slow request consumes more than one. Nothing needed to call or interpret the tool is missing.

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?

Zero parameters, so the baseline is 4. The description usefully explains the empty schema by noting the calling key is implicit and no key or account id is passed, which confirms there is nothing to supply.

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 and resource ('Reads the calling API key's own plan and usage') plus the scope constraint that no key or account id is passed. This is clearly distinguishable from the sibling tools (get_price, get_quote, list_chains, search_tokens), which are about market data rather than the caller's own quota.

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?

Explicitly names the triggering situations: answering quota or throttling questions, and checking before a long run of calls. No exclusions or named alternatives are given, but the siblings are unrelated, so the omission is minor.

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