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

Annotations already declare this as a safe, idempotent, closed-world read, so the safety burden is covered. The description adds genuine value by enumerating the payload shape (specs, included/excluded features, location, availability, billing cycles with price, setup fee, monthly equivalent and cart link), which is the behavioral detail an agent needs. It omits error/failure behavior (e.g., invalid slug or unsupported currency), which keeps it from a 5.

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?

A single front-loaded sentence: 'Everything about one plan by slug' establishes scope before the colon-delimited field inventory. No filler or restated metadata, though the dense unbroken enumeration of return fields could be marginally easier to scan if grouped.

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 carries the return-value burden and does so comprehensively, listing the substantive data the caller gets back. It is missing only failure-mode context (unknown slug, unsupported currency) that would round out a mutation-free lookup tool.

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 both slug and currency thoroughly, giving a baseline of 3. The description goes slightly beyond by framing the slug as identifying 'one plan' and by flagging that per-cycle pricing varies, reinforcing why a currency parameter matters, though it never names currency directly.

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 ('Get ... one plan by slug') and immediately scopes it to a single plan, distinguishing it from plural/sibling operations like compare_plans or search_products. An agent knows it retrieves one product record rather than a list.

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 phrase 'one plan by slug' implies the precondition that a slug must already be known, which is the main usage gate. However, the description never explicitly says when to prefer this over compare_plans or recommend_plan, and the pointer to which tools produce slugs lives in the schema, not the description.

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