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

readOnlyHint=true already tells the agent this is a safe read, so the description's burden is lower. It adds the set of returned fields and the underlying REST mapping (GET /subscriptions/{id}), but says nothing about behavior on a missing/invalid id or any auth/rate-limit constraints.

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 short sentences with zero filler; the purpose and returned fields are front-loaded, with the API mapping relegated to a trailing clause.

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, listing the returned fields is a valuable addition and covers the main completeness gap for a read-only single-entity fetch. Minor omissions remain (error behavior for unknown ids), keeping it just short of full coverage.

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?

There is one parameter with 100% schema description coverage, so the schema already documents 'Subscription id.' The description's 'by id' adds no syntax, format, or lookup semantics beyond that, making the baseline 3 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?

States a specific verb and resource ('Get a single subscription by id') and enumerates the fields returned (product, quantity, price, charge interval, next charge date). The 'single ... by id' framing cleanly separates it from the sibling list tool recharge_list_subscriptions.

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?

Usage is implied: fetch one subscription when you already have its id. There is no explicit when-to-use vs when-not guidance and no pointer to alternatives such as recharge_list_subscriptions for enumerating subscriptions, so the agent must infer the routing.

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