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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=false, so the safety profile is covered. The description adds genuinely useful context beyond that: the tool is paid ($0.001 per autonomous x402 call, or 1 direct credit), which materially affects an agent's decision to call it. It stops short of describing the return shape (single identity vs. ranked candidates) or no-match behavior.

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 sentences, each earning its place: cost disclosure, purpose, and routing. Front-loading the paid notice is appropriate for a metered tool, and the fallback routing is placed last where it reads naturally.

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 one-parameter, read-only resolution tool with no output schema, the description covers purpose, cost, and the alternative path. The notable gap is the return contract: whether a resolution yields a single canonical identity, multiple candidates, or an ambiguity error, which matters for a tool whose whole job is disambiguating uncertain names.

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% with a single parameter, and the schema already states 'Full or partial horse name' with an example. The description reinforces the partial/fuzzy matching intent ('partial or uncertain horse name'), but adds little syntax or format detail beyond what the schema provides. 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?

States a specific verb and resource ('Resolve a horse identity against Horse Truth profiles') and immediately distinguishes itself from siblings by naming horse_snapshot and horse_intelligence as the tools for the known-name case. An agent can tell exactly what this tool is for without opening the 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?

Explicit when-to-use ('when you have a partial or uncertain horse name and need the exact Horse Truth identity before other calls') and explicit when-not-to-use with named alternatives ('use horse_snapshot or horse_intelligence instead once you know the exact name'). Nothing is left to inference.

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