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

The annotations already declare readOnlyHint=true, idempotentHint=true, openWorldHint=false, and destructiveHint=false, so the description does not need to re-establish the safety profile. It usefully adds the scope of the summary and the returned fields, including guardrails and graphVersion, which is valuable context absent from structured data. It does not add further behavioral details such as response size or rate limits, but for a zero-parameter tool the annotations carry most of the burden.

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 compact sentences with no filler: purpose first, selection guidance second, return contents third. The sibling-routing information is front-loaded and makes efficient use of the space.

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 zero parameters, no output schema, and rich annotations, the description supplies everything an agent needs: what the summary contains, when to use it, and which sibling to use otherwise. Listing the return fields compensates for the missing output schema.

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?

There are no input parameters, so there is no parameter semantics for the description to clarify. The baseline for a zero-parameter tool is 4.

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 states a specific verb and resource ('Read-only summary of Nebula') and enumerates the included content areas (org, founders, services, industries, frameworks, counts). It also explicitly distinguishes itself from all three siblings, so an agent can select it without inspecting other schemas.

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 gives an explicit use case ('Use for a company snapshot') and routes each alternative case to the right sibling: ranked queries to nebula_search, browsing titles/URLs to nebula_list, and one exact path to nebula_section. This is exactly the when/when-not/alternatives guidance the dimension rewards.

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