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

Annotations already declare readOnlyHint=true and openWorldHint=false, so safety is covered. The description adds genuinely useful non-schema behavior: it costs 5 prepaid credits and requires production billing. However, it says nothing about what 'flag' produces, how staleness is determined, or error behavior when credits run out.

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 short sentences with the function stated first and the billing constraint second — no filler. Slightly clipped, but nothing is wasted.

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?

With no output schema, zero schema descriptions, and no annotations covering cost, the description should explain the input formats and what a 'stale flag' result looks like. It covers only the billing gate, leaving the agent unable to construct observed_at correctly or anticipate the response.

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 0% for both required parameters, so the description carries the full burden and mostly fails it. 'Sample age' loosely hints at maximum_age_minutes, but the expected format of observed_at (ISO 8601? epoch?) and the unit/threshold semantics are left entirely unexplained.

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 gives a specific verb pair plus resource: 'measure sample age' and 'flag stale upstream records'. That is clearly a freshness/staleness check and is distinguishable from siblings like dataset_quality or dependency_availability, though it never names a boundary against them.

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?

There is no guidance on when to use this tool versus the many other quality/availability siblings, and no preconditions beyond billing. The only conditional information is commercial ('PAID ONLY'), not situational.

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