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

Annotations already mark readOnly, idempotent, and non-destructive. The description adds meaningful context beyond that: it is 'Free to call, same on every plan', 'Descriptive market data only', and it explicitly reports streamed/free set status plus 'where recorded' for data availability. This gives the agent access, cost, and data-boundary information the annotations do not provide.

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 description is compact and front-loaded: the first sentence packs the search action, input examples, and key output fields. The following sentences add usage timing, cost/access, and scope limitations. Every sentence earns its place with no filler.

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?

An output schema exists, so return-value documentation is not the description's job. Given that, the description covers the essential selection context: when to use it, what makes it special (free, streamed/free-set flags, symbol resolution), and its limitation as descriptive market data only. Nothing needed to invoke it correctly 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?

Schema description coverage is 100%, with all four parameters documented including query, pair alias behavior, and limit defaults/ceiling. The description does not add parameter-level semantics beyond that, so the baseline of 3 is appropriate.

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: 'Search the coin catalog by symbol or part of a name'. It also distinguishes itself from siblings by naming what it returns: the canonical symbol other tools take, streaming/free-set status, and market data. This is much more precise than the generic title 'Find a coin'.

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?

Directs the agent to 'Use it first when a coin is unfamiliar or ambiguous, and for "which coins are ..." discovery.' This is a clear context for when the tool should be chosen. It does not explicitly name alternatives or when-not-to-use cases, so it stops short of a 5.

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