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

Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and destructiveHint=false, covering the safety profile. The description adds value beyond that: it discloses the matching behavior ('returns the whole slice whatever words the signals happen to use') and the exact OR/AND combination semantics with a worked example. No contradiction with annotations; the read-only claim is supported by 'select' language.

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?

Every sentence earns its place: purpose, usage examples, differentiation, facet list, and combination rules. It front-loads the core purpose and the differentiation from search_signals early. The closing locale note ('A locale filter alone cannot answer this question') is slightly cryptic and the least clearly motivated sentence, which keeps it from a 5.

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 tool with nontrivial filter semantics and five parameters, the description covers purpose, usage context, sibling differentiation, the facet vocabulary, and combination behavior. There is no output schema, and the description doesn't detail return format, but given the read-only, idempotent nature disclosed by annotations and the rich filter documentation, the agent has what it needs to call correctly. Minor gaps: return shape and how relate/limit interplay are left to the 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?

Schema coverage is 100%, so the schema already documents all five parameters, including the filter's key vocabulary and OR/AND rules. The description reinforces the filter semantics with its own example ('country:JP,country:CL domain:climate') and adds the conceptual facet-vs-text framing, which is genuinely useful. But much of the filter detail is duplicated in the schema, so the description's marginal addition over the schema is modest — the baseline 3 applies.

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 opens with a specific verb and resource: 'Select a slice of the live wire by facet tags.' It defines what 'facet tags' mean (structured metadata, not text words), and explicitly separates this tool from search_signals by the matching mechanism. An agent can immediately tell what this does and how it differs from the sibling search tool.

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 explicit when-to-use guidance: 'Use this when you can name the slice you want' with concrete examples (high-severity climate in Japan, one provider, one language). It also names the alternative and the condition that selects it: 'reach for search when you have a subject word and no category to name.' This is a textbook when/when-not pairing.

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