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

Annotations already declare readOnlyHint=true, so the safety profile is covered; the description additionally discloses catalog size differences between source modes ('account ~10-50 curated' vs 'library 10K+ searchable') and clarifies that 'he' means Hebrew-verified. It does not mention rate limits or auth requirements, but for a read-only list tool the added context is solid.

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?

Front-loaded with purpose, then triggers, then source modes, then the sibling exclusion — an efficient ordering. The telegraphic fragment style ('THIS, never null') is dense but every clause carries routing or scoping value.

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?

For a 13-parameter, zero-required, read-only list tool with no output schema, the description covers purpose, routing, source-mode semantics and filtering. Pagination is delegated to the schema (last_sort_id), which is acceptable; only return-shape expectations are left implicit.

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 92%, so the schema already documents all 13 parameters thoroughly. The description's filter summary (gender / language / category) and source-mode note largely restate what the schema says, adding only the 'he = Hebrew-verified' nuance. Baseline 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?

Opens with a specific verb+resource ('Voice catalog (ElevenLabs)') and states the tool lists voices only. It explicitly names the sibling it is not ('speaking is var2_create_dialog'), so an agent can separate it from the create/result tools without opening a schema.

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?

Provides concrete user-phrasing triggers ('what voices do you have', 'list voices', 'which voice for <language/style>', 'browse voices') and an emphatic routing rule ('→ THIS, never null'). It also names the alternative (var2_create_dialog) for the adjacent action of speaking, leaving nothing to inference.

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