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

Goes well beyond the annotations: it explains the repeat-call behavior (a second call reports the contact already existed, consistent with idempotentHint=true), the downstream enforcement effect (contact analysis refuses excluded contacts, people lists omit them), the quota exemption, and a hard rate limit of 10 new records per account per day. These are operational facts an agent cannot infer from readOnlyHint/openWorldHint.

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?

Front-loads the core action and condition, then layers safety, enforcement, cost, and limit information in short independent clauses. Every sentence carries distinct decision-relevant information; nothing is repeated from the schema or title.

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 one-parameter, no-output-schema tool, the description covers everything an agent needs: input flexibility, idempotency, enforcement consequences, cost model, rate cap, and the removal path. Nothing material is left to inference.

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% and the single parameter already documents that email, phone, or LinkedIn values are accepted and auto-detected. The description restates that same acceptance/detection behavior rather than adding format examples, normalization rules, or error cases, so it neither compensates nor detracts.

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?

States a specific verb and resource ('Record a person in this account's opt-out list') plus the triggering condition ('when they ask not to be contacted'). It also names the counterpart tool remove_opt_out, so an agent can distinguish it from the closest sibling without opening any schema.

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?

Gives explicit when-to-use ('when they ask not to be contacted'), explicit when-not-to-use ('not for bulk-marking a list'), the correct batching posture ('one at a time'), and the alternative for the inverse operation ('Use remove_opt_out to lift a record').

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