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

Annotations already declare readOnlyHint=true and openWorldHint=false, so safety is covered. The description adds real value by disclosing DST handling, but omits behavior for ambiguous/nonexistent local times during DST transitions and for invalid zone identifiers, which are the main failure modes for this operation.

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?

A single front-loaded sentence that packs purpose, input shape, defaults, and DST awareness with no filler. Nothing could be removed without losing 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?

For a simple three-parameter, read-only conversion tool with full schema coverage, the description covers input shape, defaults, and DST behavior adequately. Since there is no output schema, a brief note on the returned value's form would close the only remaining gap.

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%, so every parameter is already documented, including the UTC default for `to` and the naive-input condition for `from`. The description restates those conditions rather than adding new semantics (no zone-name format, offset rules, or edge-case handling), so baseline 3 applies.

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 verb (convert) plus a precise resource (ISO-8601 instant / naive local between IANA zones). The resource is unmistakably distinct from siblings like now, add_business_days, is_business_day, and resolve_expression, so an agent can select it without 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 description implies usage by noting naive local input requires from=, but it never states when to prefer this tool over siblings such as now or resolve_expression, nor any exclusions. Usage has to be inferred from the input shape.

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