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

Annotations already declare readOnlyHint=true, openWorldHint=true, and destructiveHint=false, so the safety profile is known. The description adds valuable behavioral context: deterministic processing, same-time grouping, future-dated ID reporting, stable counts/digests, and explicit UTC as-of usage. No contradiction with annotations.

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 two sentences that front-load the core purpose, enumerate key behaviors, and include pricing. Every phrase carries meaning—no filler, repetition, or unnecessary detail.

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 tool with nested row objects and no output schema, the description covers the main behavioral contract (sorting, grouping, future-id reporting, digests) and the central time constraint. It is somewhat vague on the exact output structure, but combined with the extensive schema descriptions, it is adequate for a moderate-complexity tool.

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 each parameter (schemaVersion, asOf, rows) is well-described in the schema, including details like 'Explicit UTC timestamp; the runtime never reads the current clock' and 'Input order is not semantic.' The tool description reinforces but does not add per-parameter meaning beyond the schema.

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 uses a specific verb ('Build') and a clear resource ('deterministic chronology'), with explicit input constraints ('1 to 30 closed US brand evidence rows and an explicit UTC as-of time'). It distinguishes itself from sibling tools by naming concrete operations: sorting, same-time grouping, future-dated ID reporting, and stable counts/digests.

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 description implies when to use the tool (when you need a deterministic chronology from US brand evidence) but provides no explicit alternatives or exclusions. It does not name sibling tools or state when not to use this tool, so it only reaches the 'implied usage' level.

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