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

Annotations already carry the safety profile (readOnlyHint, idempotentHint, destructiveHint), so the bar is lower. The description adds value beyond that by disclosing the exclusion semantics — leads blocked by do-not-contact, archived, or non-active state are counted separately and only itemized when include_excluded=true. It reinforces 'contacts no one and changes nothing' without contradicting the annotations.

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-loaded with the core purpose and scoping, then effective safety clarifications, then usage guidance and routing. Each sentence earns its place, though the length is near the upper bound — it could be tightened without losing value.

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 there is no output schema, the description compensates by describing the return shape — contactable leads under `leads` and excluded leads counted/itemized separately — which is the critical missing information. For a moderate-complexity listing tool this is sufficient to call correctly.

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%, so the baseline is 3. The description goes beyond the schema by clarifying the exact-match semantics of segment_tag and explaining the behavioral consequence of include_excluded (itemizing blocked leads versus just counting them). This adds meaning rather than repeating the property descriptions.

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 — 'List the actual leads (id, name, email) in the current company, optionally filtered to one exact segment tag' — with a clear scope. It differentiates itself from the directly relevant sibling enroll_by_segment, making it unambiguous which operation is which.

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?

Provides explicit trigger conditions ('Use when the operator says "who is in <segment>", or before enrolling/drafting for named leads') and names the alternative with the condition for choosing it ('To enroll a whole segment in one call, prefer enroll_by_segment'). A routing block further pins the intent. Nothing is left to inference.

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