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

Annotations already declare readOnly, idempotent, non-destructive, and openWorld false. The description adds extensive behavioral context beyond that: the full response shape, partial_day semantics, proof statuses and timing (stamped after 12:00 UTC), and null handling for restricted source terms. This is rich disclosure.

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 purpose is front-loaded, and no sentence is mere filler given the absence of an output schema. Still, the text is a dense single paragraph with long, semicolon-heavy sentences, which makes it harder to scan than an ideally structured definition.

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?

With no output schema, the description must carry the full burden of explaining return values, and it does: periods, bands, z-scores, first_print, seal, proof details, statuses, and timing. It also covers edge cases like partial days and nulls, so an agent has what it needs to interpret results correctly.

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 only one parameter exists, so the baseline is 3. The description adds value by enumerating all valid tickers and tying the ticker to list_indices, which goes beyond the schema's generic example.

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 opens with a specific verb-and-resource purpose: retrieving history, rules, source and proof for one index, and it names list_indices as the source of valid tickers. It clearly distinguishes this single-index lookup from the sibling list_indices, so an agent can select it without opening other tools.

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?

It explicitly says to use it for one index named by list_indices and enumerates valid tickers, establishing the context. However, it does not spell out when not to use it or contrast it with other siblings beyond the ticker-source relationship, so it falls short of a full 5.

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