Zapmail MCP Server

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

No annotations are provided, so the description carries full burden. It mentions payment processing and automatic recharge, but fails to disclose critical behavioral traits such as required permissions, whether this is a mutating operation, potential side effects, error handling, or response format. The description is insufficient for a tool that likely involves financial transactions.

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 description is concise with three sentences, front-loading the core purpose. However, the final sentence 'Invoke this endpoint' is redundant and adds no value, slightly reducing efficiency.

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?

Given the complexity of a purchase tool with no annotations and no output schema, the description is incomplete. It lacks details on behavioral aspects, error conditions, return values, and usage context, making it inadequate for safe and effective tool invocation.

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 description coverage is 100%, so the schema fully documents all 7 parameters. The description adds no parameter-specific information beyond implying a subscription plan purchase, which is already covered by the tool's name and purpose. Baseline 3 is appropriate as the schema does the heavy lifting.

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?

The description clearly states the action ('purchase') and resource ('Zapmail subscription plan'), specifying payment via wallet balance. It distinguishes from siblings like 'purchase_domains' or 'purchase_plan_25780426e0' by focusing on subscriptions, but doesn't explicitly differentiate beyond the resource type.

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?

No guidance on when to use this tool versus alternatives like 'purchase_plan_25780426e0' or 'purchase_prewarmed_subscription_25774263e0' is provided. It mentions payment method (wallet) but lacks context on prerequisites, eligibility, or comparison with other purchase tools.

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