add_duration

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

With no annotations provided, the description fully carries the behavioral disclosure burden. It explains DST boundary behavior, month-end clamping, exact elapsed time for time units, and the '-' subtraction prefix. This is exemplary transparency for a pure arithmetic 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?

The description is three sentences, front-loaded with the core action, then efficiently details edge-case behavior. Every sentence adds value; there is no filler or repetition of schema 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?

For a moderately complex tool with no annotations and no output schema, the description covers the important behavioral nuances (DST, month-end, subtraction) thoroughly. It does not mention return value format or error cases, but those are relatively predictable for this operation, so the gap is minor.

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 baseline is 3. The description adds meaningful semantics beyond the schema by explaining how duration units behave (calendar-aware vs exact elapsed time) and how timezone affects wall-clock arithmetic, which enriches the parameter meanings.

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 opens with a specific verb and resource: 'Add an ISO-8601 duration to a timestamp, in a timezone.' It clearly distinguishes this arithmetic tool from siblings like time_between (difference), convert_timezone (zone conversion), and get_current_time (current time).

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 description gives clear context for when the tool is appropriate—duration arithmetic with calendar-aware behavior—but it does not explicitly name alternatives or state when not to use it. Sibling tool names imply the differentiation, but the description itself offers no direct guidance.

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