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

The annotations already establish this is a pure read-only, closed-world computation, so the description doesn't need to prove safety. What it omits is still behavioral: it doesn't say the result is start + ttl normalized to UTC, whether the return is an ISO-8601 string, or how invalid/negative TTLs and malformed timestamps are handled.

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?

One short sentence, front-loaded with the returned value, with no redundant or filler wording. Nothing could be removed without losing meaning.

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?

This is a simple two-parameter pure function, so the bar is low, but with no output schema and no schema descriptions the definition should at least pin down input format and return format. It is adequate to identify the tool but leaves the agent guessing on exact string formats and edge-case behavior.

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 0%, so the description carries the full burden of explaining parameters, and it only says 'supplied timestamp' and 'time-to-live'. It never states that start_iso must be ISO-8601 formatted with a timezone, nor that ttl_seconds is an integer count of seconds, leaving both parameters documented only by their names.

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 gives a specific verb and result ('Return UTC expiration') plus the two inputs that produce it, which is enough to distinguish it from sibling window/planning utilities like privi_backoff_window. It falls short of 5 only because it never contrasts itself with those siblings explicitly.

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 statement of when to use this versus alternatives, no prerequisites, and no exclusions. The mention of 'supplied timestamp and time-to-live' only restates the required inputs rather than giving situational guidance.

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