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

The description mentions the comment is 'visible in its activity log', adding behavioral context beyond the annotations (which only have destructiveHint: true). It also states 'WRITE', which is consistent with destructiveHint. This additional detail helps the agent understand the side effect.

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 one sentence plus the endpoint, very concise. It front-loads the action. However, it could be slightly more structured (e.g., separate purpose from endpoint). No waste, but also minimal.

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 simple write tool with no output schema, the description is adequate but lacks information on return behavior or error handling. The context of activity log is helpful. Given low complexity, it meets a minimum viable level.

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 coverage is 100% with each parameter having a minimal description. The tool description does not add extra meaning beyond the schema. Baseline is 3, and no additional parameter context is provided.

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 it adds a comment to an invoice, with the verb 'adds' and resource 'comment to an invoice'. The title matches. This is distinct from sibling tools like mercoa_create_invoice or mercoa_update_invoice, which create or update invoices rather than adding comments.

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 includes 'WRITE' indicating it's a mutation, but does not explicitly state when to use this tool versus alternatives. There is no guidance on prerequisites (e.g., invoice must exist) or when not to use it. The sibling list provides context but the description lacks explicit usage direction.

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