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

Annotations already declare readOnlyHint=true and openWorldHint=false, so safety and scope are covered. The description goes beyond that by disclosing the returned fields and, importantly, the meaning of coinsBasis (reported by issuer vs estimated from net assets/coin price) and the presence of 7-/30-day changes and 30 days of daily history — meaningful disclosure for an agent interpreting results.

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 the core output and scope, then the per-fund breakdown and history. Two dense sentences with no filler, though the second sentence packs several schema-adjacent terms (coinsBasis, supplyPct) that make it heavier than necessary for a single-parameter tool.

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?

For a one-parameter, read-only tool with no output schema, the description fully carries the return-value burden: totals, per-fund coins, share metrics, basis provenance, and the change/history windows. An agent can decide to call it and interpret the response correctly from this text alone.

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 coverage is 100% and the single parameter is an enum of 16 tickers with its own description, so the schema does the heavy lifting. The description adds only the marginal note that omitting the filter returns all 16, which is the baseline-3 level of added value.

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 — the coins held in trust by US spot crypto ETFs — and defines the scope (one asset or all 16) plus the derived metric supplyPct. It is clearly a holdings-snapshot tool, implicitly distinct from flow-oriented siblings like get_fund_flows, but it never names an alternative to sharpen the boundary.

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 'one asset or all 16' phrasing implies the optional-filter usage (omit asset for the full ETF universe), which is useful. However, there is no explicit when-to-use/when-not guidance and no mention of the neighboring tools (get_fund_flows, get_funds) an agent would weigh this against.

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