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

With no annotations, the description carries the full burden, and it does disclose the paid x402 pricing model ($0.001/call in USDC on eip155:8453), which is real behavioral context. However it says nothing about boundary semantics (whether end is inclusive), timezone assumptions for the ISO dates, handling of start > end, or error behavior.

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, front-loaded with the compute description followed by the pricing note; every clause carries information. The pricing sentence is somewhat disjunctive from the functional description but is justified for a metered tool.

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 two-param calculator with no output schema, the description usefully describes the return shape (total days, weeks+days, years/months/days), filling the gap left by the missing output schema. It is nearly complete; only edge-case semantics are missing.

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% with only two params, so the schema already documents 'start' and 'end' as ISO YYYY-MM-DD strings. The description adds no syntax, range, or ordering detail beyond that, 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?

States a specific verb+resource ('count the total days between two dates') and enumerates the three output breakdowns, which tells an agent exactly what the tool computes. It implicitly distinguishes itself from the calendar-counting siblings, though it never names live_business_days, the closest functional alternative.

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?

Usage is only implied: an agent can infer this is the tool for calendar-day spans, but there is no explicit when-to-use guidance or exclusion. The most valuable guidance here – that this counts calendar days while live_business_days counts working days – is absent.

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