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 mentions 'Upgrade an existing subscription', implying a mutation, but fails to describe critical behaviors such as whether this requires authentication, what happens to billing cycles, if changes are reversible, or potential rate limits. The phrase 'Invoke this endpoint' adds no meaningful context, leaving significant gaps in transparency.

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, stating the purpose in the first sentence. However, the second sentence ('Invoke this endpoint.') is redundant and adds no value, slightly reducing efficiency. Overall, it is appropriately sized but could be more streamlined.

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 mutation tool with 7 parameters, no annotations, and no output schema, the description is incomplete. It lacks details on behavioral traits (e.g., side effects, error handling), usage context, and output expectations. While the schema covers parameter types, the description does not compensate for the absence of annotations or output schema, making it inadequate for informed 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?

The description specifies two parameters ('new plan key' and 'subscription ID'), but the input schema has 7 parameters with 100% schema description coverage, including overrides like 'method' and 'path'. The description does not add semantic meaning beyond the schema, such as explaining how 'plan key' relates to subscription tiers or the format of 'subscription ID'. With high schema coverage, the baseline score of 3 is appropriate, as the description provides minimal additional value.

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 ('Upgrade an existing subscription') and specifies the required inputs ('by providing a new plan key and the subscription ID'), which distinguishes it from sibling tools like 'cancel_subscription_13489478e0' or 'purchase_subscription_25771049e0'. However, it does not explicitly differentiate from 'upgrade_dns_shield_ltd_plan_25782123e0', which might be a similar upgrade operation for a different resource.

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 no guidance on when to use this tool versus alternatives, such as 'cancel_subscription_13489478e0' for ending a subscription or 'purchase_subscription_25771049e0' for new purchases. It also lacks prerequisites, like whether the subscription must be active or if specific permissions are required, leaving usage context unclear.

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