Apollo 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. It discloses the tool's behavior as a preview/testing operation with variable substitution, which is helpful. However, it doesn't mention important behavioral aspects like whether this requires authentication, has rate limits, affects system state, or what happens when contact_id is omitted. The description adds value but leaves 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 perfectly structured and front-loaded: first sentence states core purpose, second explains usage context, then parameter documentation, and finally return value. Every sentence earns its place with zero waste. The formatting with clear sections enhances readability.

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 3 parameters with 0% schema coverage and an output schema exists, the description does well by explaining parameter semantics and the tool's purpose. However, as a testing/preview tool with no annotations, it should ideally mention more about the preview output format, error conditions, or authentication requirements to be fully complete.

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 schema description coverage is 0%, so the description must compensate. It provides meaningful semantics for all 3 parameters: explains that subject and body_html can include {{variables}}, and that contact_id is optional for previewing with real data. This adds crucial context beyond the bare schema, though it doesn't specify variable syntax details or contact_id format.

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 with specific verbs ('preview', 'test') and resources ('email', 'contact data'), and distinguishes it from siblings like email_send by focusing on preview/testing rather than actual sending. The mention of variable substitution adds specificity.

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 clear context for when to use this tool ('test how your email will look with real contact data'), but doesn't explicitly state when NOT to use it or name specific alternatives. It implies usage for testing before sending, but lacks explicit exclusions or named sibling comparisons.

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