Zapmail MCP Server

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

No annotations are provided, so the description carries the full burden of behavioral disclosure. It states this is a purchase operation (implying a write/mutation) and mentions payment via 'wallet balance,' but doesn't cover critical behaviors: whether this is idempotent, what happens on insufficient balance, if it requires specific permissions, rate limits, or what the response looks like. For a financial transaction tool with zero annotation coverage, this is a significant gap.

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 appropriately concise and front-loaded: the first sentence states the core purpose, followed by additional context about pre-warmed plans. However, the final sentence 'Invoke this endpoint.' is redundant and adds no value. Otherwise, it's efficient with minimal waste.

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 (a purchase tool with financial implications), lack of annotations, and no output schema, the description is incomplete. It misses essential details: error conditions, response format, authentication requirements, and how it differs from sibling purchase tools. The context about pre-warmed plans is useful but insufficient for safe and effective use by an AI agent.

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 already documents all 7 parameters (e.g., 'method', 'path', 'body'). The description doesn't add any parameter-specific details beyond what's in the schema—it doesn't explain which parameters are relevant for this purchase operation or their expected values. With high schema coverage, the baseline is 3, as the description doesn't compensate but also doesn't detract.

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 tool's purpose: 'purchase a pre-warmed subscription plan using your wallet balance.' It specifies the verb ('purchase'), resource ('pre-warmed subscription plan'), and payment method ('wallet balance'). However, it doesn't explicitly differentiate from sibling tools like 'purchase_subscription_25771049e0' or 'purchase_plan_25780426e0', which likely handle different subscription types.

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 provides minimal usage guidance. It mentions that pre-warmed plans include 'aged domains with warmed-up mailboxes ready for immediate use' and ensure 'better email deliverability,' which implies when this tool might be preferred. However, it doesn't specify when to use this versus alternatives (e.g., regular subscriptions), prerequisites like sufficient wallet balance, or any exclusions. The guidance is implied rather than explicit.

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