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

With no annotations, the description carries the full burden. It discloses the data is continuously recorded and covers the past, and explains the output composition (percentages and incident windows). However, it omits specifics like sampling frequency, exactly how degraded vs. major outage are defined, or any data delay/limitations for tracked services.

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?

Three sentences: what it does, when to use it, and underlying data. Each sentence earns its place with no redundancy. The purpose and usage are front-loaded, making it easy to scan.

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?

No output schema exists, but the description explains the return structure (percentages and incident window list) and the data source (continuously-recorded series). It lacks details on timezone, aggregation granularity, or response format, but for a simple history tool with 2 well-described parameters, it is reasonably complete.

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 both service and days are already well-documented. The description adds example context ('this month' maps to days) but no new parameter syntax or edge cases beyond what the schema provides. 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 it provides service reliability over time with percentages and incident windows. It explicitly contrasts with a status page (sibling check_service_status), and example queries like 'how often has Vercel gone down this month' clarify the tool's distinct purpose.

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?

It explicitly says 'Use for questions a status page cannot answer' and gives concrete example use cases, effectively excluding real-time status checking. However, it does not name the exact alternative sibling tool, though check_service_status is implied by the context.

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