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

No annotations exist, but this is a pure computation with no side effects, so the risk burden is low. The description does disclose the return content (seconds and a breakdown), which is the main behavioral fact an agent needs; however, it says nothing about timezone handling in ISO inputs or how reversed/equal datetimes are treated.

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 with zero padding: it names the input format and the output shape in one pass. Nothing is wasted and nothing essential is buried.

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?

With no output schema and no annotations, the description correctly carries the return-value burden by describing both the total-seconds and breakdown outputs. For a simple two-input computation this is nearly sufficient; only timezone parsing and invalid/reversed interval handling are 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 0% and the schema only labels the nested fields 'Start' and 'End' as plain strings. The description compensates by stating they are ISO 8601 datetimes, which is genuinely useful format information, but adds no ordering/validation semantics (e.g. whether end must be after start) or error behavior for malformed input.

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?

Names a specific computation (duration between two ISO 8601 datetimes) and even states the return shape (total seconds plus a d/h/m/s breakdown). It is clearly distinct from siblings like time_add or time_humanize, though it never explicitly contrasts 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 guidance on when to use this versus time_add, time_humanize, or time_convert, nor any prerequisite or edge-case note (e.g. end before start). The agent must infer all of that from the vague family of time_* siblings.

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