Zapmail MCP Server

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

With no annotations, the description carries full burden. It discloses payment behavior (automatic deduction from wallet) and hints at a transactional endpoint, but lacks critical details like required permissions, whether the purchase is reversible, error conditions, or response format. This is inadequate for a financial transaction tool.

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 brief and front-loaded with the core purpose, but the second sentence about payment adds value, and the third ('Invoke this endpoint.') is redundant and could be omitted. Overall efficient with minor 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?

For a purchase tool with no annotations and no output schema, the description is insufficient. It misses key behavioral aspects like confirmation steps, return values, error handling, and doesn't compensate for the lack of structured safety or output information, leaving significant gaps for agent 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 purchase action, which doesn't enhance understanding of individual parameters. Baseline 3 is appropriate as the schema handles parameter documentation.

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 ('a placement test subscription plan'), specifying plan types (Monthly or LTD). It distinguishes from siblings like 'purchase_domains' or 'purchase_subscription_25771049e0' by focusing on placement test plans, but doesn't explicitly contrast them.

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 mentions payment is deducted from wallet balance, implying a prerequisite, but provides no explicit guidance on when to use this tool versus alternatives like 'purchase_placement_test_25780176e0' or 'purchase_subscription_25771049e0'. No exclusions or clear context for selection are given.

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