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

Annotations already declare readOnlyHint=true and destructiveHint=false, lowering the bar. The description adds valuable context: determinism ('deterministic routing plan', 'reproducible digests'), side-effect-free behavior ('never sends messages, calls destinations, fetches URLs'), and the closed-world constraint ('or infers identity'). It also discloses pricing, which is beyond annotations.

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?

The description is two sentences with the main action front-loaded. The first sentence packs the core purpose and outputs without waste; the second sentence adds essential side-effect exclusions and pricing. Every phrase earns its place, and the structure is efficient.

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?

Given the tool's moderate complexity (4 top-level parameters, two nested array types) and rich schema, the description is complete enough. It describes the high-level behavior and lists the key output components, which is important since there is no output schema. The exclusion of identity inference and side effects further clarifies boundaries. A full output structure description would push it to 5, but the current level is solid.

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 100%, so the baseline is 3. The description adds minimal parameter semantics beyond the schema: it refers to 'normalized US brand signals and ordered rules' as the inputs, but the schema already documents each property with detailed descriptions, enums, and constraints. The description does not need to compensate for missing schema info.

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: turning normalized US brand signals and ordered rules into a deterministic routing plan. It enumerates specific outputs (matched routes, unmatched IDs, counts, warnings, digests) and explicitly differentiates itself from sibling tools by noting it never sends messages, calls destinations, fetches URLs, or infers identity.

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 provides clear context for when to use this tool: when you need a deterministic routing plan from signals and rules. It also gives exclusions via 'never sends messages, calls destinations, fetches URLs, or infers identity,' implying alternatives are needed for messaging or identity inference. However, it does not explicitly name alternative tools or state 'use when...' versus 'do not use when...'.

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