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

Annotations already declare readOnly/idempotent/non-destructive, and the description still adds substantial context: Early access status, required billing read scope on a Last Price credential, the claimed-workspace prerequisite with the specific 403 refusal, and renewal semantics including rollover credits.

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?

Front-loads the purpose and returned fields, then lifecycle, then prerequisites and failure mode. Most sentences carry unique information; the standalone 'Early access.' fragment is slightly disruptive but still earns its place as a caution signal.

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 compensates by enumerating the response fields, and it covers the auth/workspace prerequisites and the 403 error path. An agent has everything needed to call this correctly without further reading.

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 per calibration the baseline is 3, but the description goes slightly beyond by tying plan_id to its source tool and implying the status filter values via the 'active'/'cancelled' framing ('why it was cancelled'). Pagination semantics 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+resource (list subscriptions on a recurring credit bundle), the supported cadences, the sort order ('newest first'), and the exact fields returned. An agent can distinguish it from list_credit_bundle_plans or cancel_credit_bundle_subscription without opening any 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?

Gives clear context for invocation: plan_id must come from list_credit_bundle_plans, and the lifecycle note ('granting a recurring bundle starts one') explains when subscriptions exist. It stops short of explicit exclusions or naming sibling tools for adjacent tasks, so a 4 rather than 5.

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