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

With no annotations, the description carries real weight and mostly delivers: it discloses the 1 CRD cost per call, the notable rule that a rejected call still costs credits except on 429 RATE_LIMITED, the 100-row cap with no pagination mentioned, and that error payloads carry a request_id to quote to support. What it omits is auth/permission scope and confirmation that the operation is read-only, which would complete the picture on a credits-consuming endpoint.

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?

The opening clause leads with purpose, scope, and returned fields, and the following sentences each carry a distinct operational fact (status alias, cost model, error handling). It is dense and slightly parenthetical-heavy, but no sentence is redundant.

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 6-parameter read tool with no output schema and no annotations, the description covers the things an agent cannot infer: result cap, billing side effect, and error recovery path. Missing pieces are minor but real — no note on pagination behavior beyond the 100 cap and no statement of the permission scope required to list subscriptions.

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 baseline is 3; the description earns an increment by clarifying that status="active" is a convenience alias covering active, trialing and past_due rather than an exact Stripe status. It adds no meaning for email, user_id, project_id, or x402_payment, which are left entirely to the schema.

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 ("List recurring credit subscriptions") and immediately enumerates the fields returned, so an agent knows exactly what this yields. The scope constraint "newest 100" and the filterable status field further pin it down, and it is unmistakably distinct from sibling mutators like cancel_subscription and update_subscription_quantity.

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 by the resource but never stated: there is no "use this when you need X" framing and no routing to alternatives such as get_transactions, get_users, or cancel_subscription. The only explicit conditional guidance is the status="active" mapping, which is about semantics rather than when to pick this tool.

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