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

Annotations already declare readOnlyHint, idempotentHint, and openWorldHint, so the safety profile is covered. The description adds genuinely new behavioral context the annotations lack: it is a paid call costing 0.10 USDC and returns a full board in one request. It still says nothing about authentication or rate limits, keeping it short of a 5.

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 fragments with the cost front-loaded and zero filler. Efficient, though the second fragment is terse enough that a reader must infer the subject (the tool returns the fixings) from the name.

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 low-complexity, single-optional-parameter read tool with an output schema, the description plus annotations cover what an agent needs to invoke it, and the cost disclosure is a useful extra. The main omission is sibling routing, which is scored under usage guidelines.

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% and there is only one optional parameter ('day', YYYY-MM-DD, default latest), so the schema already documents it fully. The description adds no format or default detail beyond that, making the baseline 3 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?

The description states a specific resource and scope: every ticker's fixing for one day, delivered in a single call. The phrase 'every ticker's fixing for one day in one call' implicitly distinguishes it from single-ticker siblings like index_fixing, but it never names them explicitly, so the differentiation is inferred rather than stated.

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 guidance on when to use this tool versus index_fixing, index_history, or the other index_* siblings, and no stated exclusions. The only context given is the cost, which is pricing, not usage routing.

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