Pay: plans get

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

Annotations already declare readOnlyHint=true and openWorldHint=false, so 'Read-only' merely repeats structured data. The real added value is the enumeration of exactly what the call returns, which substitutes for the missing output schema and tells the agent what data it will get back. It still omits error behavior for a non-existent or inaccessible plan id.

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, front-loaded with the core action before the detail. The longer field enumeration in sentence two earns its place because no output schema exists to carry that information, and the alternative tool is named last.

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 tool whose safety profile is fully covered by annotations, the description supplies the return contents, the discovery path for the id, and the sibling to use for browsing. Nothing essential to correct invocation is missing.

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% and the single `id` parameter is already documented as an integer discoverable via pay_plans_list. The description's 'by id' adds nothing beyond the schema, so the baseline 3 for full schema coverage is correct.

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?

Specific verb+resource ('Show one plan by id') scoped to a single project subscription plan, and it enumerates the exact contents of the record (type, price/interval, trial, Stripe product name/description, reference, Apple product and subscription group ids, active flag). This clearly separates it from pay_plans_list without opening either 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?

The description explicitly routes the agent to the alternative: 'browse plans with `pay_plans_list`', and the schema reinforces this with 'Find it with pay_plans_list.' It clearly establishes the single-item vs browse split, though it states no exclusions or preconditions (e.g., what happens if the id is unknown).

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