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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so safety is covered. The description adds two genuinely useful behavioral facts the annotations do not: the per-call cost and the earliest available data date. Auth requirements and any rate limits remain unstated.

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?

Two short sentences with zero filler; the cost disclosure is front-loaded before the data description. Every clause carries information.

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 values need no explanation. Cost, granularity and data start are covered; only the behavior of the from/to range (defaults, maximum span) is 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?

Schema description coverage is 100%, so the schema already documents ticker, from and to formats. The description's phrase 'daily fixings' adds granularity meaning and the snapshot date gives context for the from range, but no syntax or default-range behavior is supplied beyond the schema baseline.

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 resource (daily fixings for a token ticker) and scope (from the first snapshot 2026-09-14), so the agent knows it returns a historical series. It does not explicitly contrast with sibling tokens_fixing or tokens_board, so an agent must infer that history differs from a point-in-time fixing.

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 pricing disclosure (0.05 USDC per call) gives a cost/usage signal, and the start date implies historical lookups. However, it never states when to choose this over tokens_fixing, tokens_board, or tokens_quotes, leaving the alternative-selection guidance to inference.

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