time_between

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

With no annotations, the description carries the burden. It discloses output breakdown (days/hours/minutes/seconds), a human-readable summary, consistent sign behavior, and a direction field. It does not cover edge cases like invalid timestamps or DST, but the disclosed details give good behavioral context.

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 sentences, both information-dense. The first delivers the core purpose, the second highlights the sign and direction semantics. No redundant or filler content.

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?

Even without an output schema, the description covers the main return components and behaviors. The tool is relatively simple, and the described details are sufficient for an agent to understand what will come back. Minor gaps like exact return type or error handling prevent a perfect score.

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 100%, so the schema fully documents all three parameters. The description adds no extra parameter-level meaning beyond restating the concept of the interval; baseline of 3 is appropriate.

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 clearly states the tool computes 'exact elapsed time between two ISO-8601 timestamps', which is a specific verb-resource combination. It also distinguishes from siblings like add_duration or convert_timezone by focusing purely on time intervals.

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 purpose is self-evident: when an agent needs elapsed time between two timestamps, this is the tool. However, it does not explicitly call out when not to use it or mention alternatives, so it misses the bar for explicit guidance.

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