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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is covered and there is no contradiction. The description adds useful output-content context (name spellings, position, length, composed reading) but does not disclose operational behavior such as not-found handling or any response edge cases.

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 sentences, with the action and core output in the first and concrete use cases in the second. There is no filler, repeated title text, or schema duplication.

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 simple read-only lookup with no output schema, the description gives enough orientation: it names the exact resource, the id input, and the main fields returned. It remains slightly ambiguous what a 'composed reading' contains and does not hint at error/not-found behavior, so some agent-facing uncertainty is left open.

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?

The schema already documents all three parameters, including enums, defaults, and the compact format, so the description does not need to add parameter-level detail and earns the baseline 3. The description's phrase 'by id' confirms the sole required parameter but adds no new semantics 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 opening verb 'Retrieve' plus the object 'one of the nineteen Haab periods by id' states exactly what the tool does, and 'by id' distinguishes it from the plural Haab-months sibling without restating the tool name. It also names the returned data, so an agent knows the resource and result before opening the schema.

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 second sentence gives concrete contexts ('calendar detail pages' and 'labeling a Haab date a chart route has already returned'), which makes the intended call sites clear. It does not explicitly name the alternative plural list route or state when not to use this tool, so it falls just short of full routing guidance.

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