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

No annotations are provided, so the description carries the burden. It does add genuine behavioral context by disclosing a paid x402 endpoint at $0.01/call in USDC on eip155:8453, and it describes the three output formats. It omits what happens if end precedes start, timezone assumptions, and any 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?

The first sentence is front-loaded and information-dense, but the second sentence is a redundant, ungrammatical restatement of the same idea and could be replaced with routing guidance. The pricing note is compact and useful.

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-parameter, no-annotation, no-output-schema tool, the description covers the return shape (total days, weeks+days, years+months+days) and the payment requirement, which is what an agent most needs. Remaining gaps are edge-case behavior rather than core calling information.

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 100% and both parameters already carry "ISO format YYYY-MM-DD" descriptions, so the schema does the heavy lifting. The description adds no additional meaning about start/end semantics (ordering, inclusivity of endpoints).

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 days between two dates) and enumerates the three breakdown formats returned. It is clearly distinguishable from a plain age calculator or a business-days tool, but it never names which sibling to prefer for related needs.

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?

"Use this when an agent needs to days, weeks and calendar time between two dates" gives implied usage, but the sentence is grammatically broken and simply restates the purpose. No exclusions are offered, e.g. that business-day counting belongs to live_business_days or that durations belong to dev_iso_duration.

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