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

Annotations already declare readOnlyHint=true, so the read-only nature is covered. The description adds useful behavioral context beyond that: no API key required, USD pricing, annual billing discount terms, Pro-tier threshold for API/MCP access, and a pointer to the checkout sibling. This exceeds the minimum for a read-only informational 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?

Four concise sentences, each with a distinct job: stating purpose, explaining when to call, specifying key pricing facts, and directing to the checkout sibling. The most important discriminator ('call this first if...') is front-loaded, and there is no filler or repetition.

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?

The description is complete for this tool type: it identifies the resource, explains its relevance to a common refusal scenario, notes the key billing terms, and tells the agent where to go next. With no parameters and a provided output schema, there are no meaningful gaps for an agent to call this tool correctly.

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?

The tool has zero parameters, so there is no parameter semantics burden for the description. The schema already covers 100% of the (empty) parameter space, and the description provides relevant context such as 'No API key needed' and pricing details, which is more than enough for a no-argument tool.

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 the tool's purpose with 'What Rayana AI costs and what each tier unlocks' – a specific resource (pricing plans) and what it provides. It also distinguishes itself from the sibling rayana_ai_start_checkout by noting that checkout converts a plan choice into a purchase link, so an agent can tell them apart.

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 explicit usage guidance: 'call this first if a research tool refused you for want of one [API key]' and 'No API key needed'. It also routes to an alternative, rayana_ai_start_checkout, for turning a choice into a link, making both when-to-use and next-step behavior clear.

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