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

Annotations already declare readOnlyHint=true, destructiveHint=false, openWorldHint=false, so the safety profile is covered. The description adds non-obvious economics: no paid entitlement is consumed, no raw provider records are exposed, and the default horse is chosen once a day by a published rule. It stops short of stating any rate limits or freshness/caching behavior for the teaser.

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-loads the key qualifier ('FREE') and orders information well: what it returns, the alternate mode, the cost/privacy guarantees, then the routing guidance. Slightly redundant across 'FREE', 'before paying', and 'no paid entitlement is consumed', but each sentence carries real content.

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?

No output schema exists, and the description compensates by characterizing the return: a real derived proof vs. a public teaser, plus paid next-action recommendations. With annotations covering safety and a single fully documented parameter, the definition is nearly sufficient; only the teaser's exact shape and any rate/freshness limits 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 100% and the single 'horse' parameter's description already states that omitting it yields the default sample proof and passing a name yields only the free public page teaser. The tool description restates the same semantics without adding format, validation, or fallback behavior for unrecognized names, so the schema does the heavy lifting.

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?

Names a concrete resource and two distinct outputs: a real derived Horse Truth proof for today's default sample horse, plus the cheapest exact paid next actions, and an alternate mode (free public teaser) when a horse name is passed. An agent can distinguish it from horse_intelligence or horse_snapshot without opening any 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?

Explicitly states when to use it ('to see a real example result, or the free public teaser for one horse, before paying') and routes the agent elsewhere by name: discover_purchase_options for payment, horse_intelligence for the full paid read. Both the trigger and the alternatives are stated, not implied.

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