Zapmail MCP Server

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

With no annotations provided, the description carries the full burden of behavioral disclosure. It states that assigning domains leads to mailbox transfers, implying a write operation, but lacks critical details: whether this requires specific permissions, if it's idempotent, what happens on failure, or any rate limits. The description is too vague for a tool that likely modifies account state, leaving significant behavioral gaps.

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 and front-loaded, with two sentences that directly state the tool's purpose and outcome. The third sentence ('Invoke this endpoint.') is redundant but doesn't significantly detract. Overall, it's efficient with minimal waste, though it could be slightly more structured by separating purpose from invocation.

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 tool's complexity (7 parameters, no annotations, no output schema), the description is inadequate. It lacks details on behavioral traits, error handling, prerequisites (e.g., needing a pre-warmed subscription), and doesn't explain the relationship between domains and slots. For a tool that likely involves account modifications, more context is needed to ensure safe and correct usage.

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?

The input schema has 100% description coverage, so the schema fully documents all 7 parameters (e.g., method, path, body). The description adds no parameter-specific information beyond implying domain assignment, which doesn't clarify how to use the schema parameters effectively. This meets the baseline of 3, as the schema does the heavy lifting, but the description doesn't enhance understanding of parameter usage.

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: 'assigns pre-warmed domains to fill available slots in your pre-warmed subscription' and mentions that 'mailboxes are automatically transferred to your account.' It specifies the verb (assign), resource (pre-warmed domains), and outcome (mailbox transfer). However, it doesn't explicitly differentiate from sibling tools like 'assign_new_mailboxes_to_domains_13490321e0' or 'get_prewarmed_domains_25774188e0', which prevents a perfect score.

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 guidance: it mentions 'available slots in your pre-warmed subscription,' implying usage when slots exist, but offers no explicit when-to-use rules, prerequisites, or alternatives. It doesn't clarify when to use this versus similar tools like 'assign_new_mailboxes_to_domains_13490321e0' or 'purchase_prewarmed_subscription_25774263e0', leaving the agent with insufficient context for decision-making.

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