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

Annotations already declare readOnly, idempotent, non-destructive, closed-world, so safety needs no restating. The description adds the useful behavioral fact that this is a lightweight summary endpoint and detail lives elsewhere. It says nothing about pagination, result count, or whether an empty result set is possible when filters match nothing.

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?

Two sentences, no filler, with the returned fields listed compactly and the cross-reference to the detail tool placed last. The colon-and-enumeration structure is easy to parse. Minor wasted lead-in on 'BillyGo's carom billiards practice patterns' before the useful 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?

With no output schema, the description shoulders the burden of describing returns and does so by naming every field. It covers the sibling relationship and the three optional filters are fully documented in the schema. Only pagination and empty-result behavior are absent, which is a small gap for a simple read-only list.

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%; lang, category, and difficulty all carry descriptions with examples, and the description only echoes the category examples already in the schema. No additional semantics such as filter combination behavior or whether unknown values error out. Baseline 3 applies when 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?

The description states the resource (carom billiards practice patterns) and enumerates the fields each entry carries (id, title, subtitle, category, difficulty), so an agent knows exactly what a call yields. It is distinguishable from billygo_get_pattern, which is named as the detail fetch. It stops short of a crisp verb like 'list' in the description itself, relying on the name/title for that.

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 routes the agent: use this to see pattern summaries, use billygo_get_pattern for the goal, idea, and coaching tip. That is a clear this-vs-alternative split. It gives no guidance on when not to use it or on combining filters, so it falls short of a 5.

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