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

With no annotations and no output schema, the description carries the full behavioral burden. It does disclose useful context ('current UTC time' for now), but it omits return formats, whether diff is signed or which argument is subtracted from which, the default unit for diff, and error behavior for malformed dates.

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 dense sentence with the four operations front-loaded and each gloss kept to a few words. No filler; the only mild cost is that packing everything into one sentence makes per-operation detail hard to find.

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?

Six parameters with no required fields, no annotations, and no output schema is a lot of ambiguity to resolve. The description names the operations but never maps required parameters per operation or describes return shapes, leaving the agent to guess how to call diff or weekday correctly.

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 50%, so the description must compensate and it only partly does: it ties 'date' to add/weekday and 'value' to add, but says nothing about date1/date2, nor how 'unit' applies across operations. The remaining parameters are undocumented in both places.

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 resource (date utilities) and enumerates four concrete operations with one-line glosses, so an agent can tell what the tool does at a glance. It does not differentiate from siblings like unit_convert, but those are unrelated enough that differentiation isn't critical here.

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 operation list implies which mode to select ('add' for duration arithmetic, 'diff' for two-date comparison, 'now' for current time), which is enough to pick an operation. There is no explicit when-not guidance and no statement of which parameters are required for which operation, so usage is only implied.

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