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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is fully covered. The description adds that results include item counts per domain, which is content-level context rather than behavior. It says nothing about ordering, whether the list is exhaustive or filtered, or how the optional product scope affects results.

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?

One sentence, front-loaded with the action and resource, with the numeric scope and downstream consumers packed in without filler. Every clause adds information.

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?

An output schema exists, so return-value structure needn't be described, and annotations cover the safety profile. The remaining gap is the entirely undocumented "product" parameter and no indication of whether the 261-domain listing is complete or scoped when that parameter is supplied.

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 the single "product" parameter, so the description carries the full burden — yet it never mentions the parameter at all. An agent cannot tell whether "product" narrows the 261 domains, filters counts, or is a display toggle.

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 and resource ("List the corpus domain lanes") and quantifies scope (261 domains of repos, docs, code examples, issues) with item counts. It also positions itself relative to siblings by calling itself "the discovery index for corpus_route and corpus_item," though it doesn't distinguish itself from the more similarly named search_corpus.

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?

Naming itself the discovery index for corpus_route and corpus_item implies a browse-then-route workflow, which is useful context. However, there is no explicit "use this first when you don't know the domain" instruction, no when-not guidance, and no mention of search_corpus as an alternative entry point.

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