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

With no annotations, the description carries the disclosure burden and does so well for the output contract: it explains that components share one sign so they sum correctly and that a `direction` field of 'past'/'future'/'same' is returned. It does not address behavior on invalid or unparsable timestamps, which is the main remaining gap for a pure computation tool.

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 tight sentences, zero filler, with the core operation front-loaded and the output/sign semantics following immediately. Every clause carries information an agent cannot get from the name alone.

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?

There is no output schema, so the description must describe the return value — it does, covering the component breakdown, the human-readable summary, and the direction field. Only edge-case behavior (invalid timestamps, whether the result is absolute or signed per direction) is left unstated.

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%, with each of `from`, `to`, and `timezone` documented in-schema including the default-to-UTC rule. The description adds no parameter-level detail beyond restating that inputs are ISO-8601 timestamps, so the 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?

The description states a specific verb+resource: computing exact elapsed time between two ISO-8601 timestamps, and it names the output shape (days/hours/minutes/seconds plus a summary). It is clearly distinct from siblings like add_duration and get_current_time, though it never explicitly contrasts itself with them.

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 tool versus add_duration (which also deals with durations) or convert_timezone. Usage is only inferable from the stated purpose; no prerequisites, exclusions, or alternatives are mentioned.

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