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

Annotations already declare idempotentHint=true and destructiveHint=false, so the safety profile is covered. The description adds valuable behavioral context: partial updates only, the lead can be identified by either lead_id or phone_number, and custom field slugs not defined on the account are ignored and reported back. This goes beyond the annotations and helps the agent predict side effects.

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?

Three sentences with no waste. The core action and field list are front-loaded, the identification and partial-update semantics come next, and the sibling routing is at the end. Every sentence earns its place.

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 10-parameter tool with no output schema, the description covers the essential invocation semantics: what fields can be updated, how to identify the lead, partial-update behavior, and how to route to siblings. It doesn't describe the return value, but with no output schema and idempotentHint=true, that's a minor gap. The custom_fields behavior is well explained.

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 baseline is 3. The description adds meaning beyond the schema by explaining the partial-update behavior, the lead_id-or-phone_number identification requirement, and the custom_fields behavior (ignored/reported back). It also tells the agent to call get_lead to discover available slugs, which is genuinely useful parameter-level guidance.

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 states a specific verb ('Update') and resource ('a lead's profile fields'), enumerates the exact fields, and explicitly distinguishes itself from sibling tools like update_stage and add_tag/remove_tag. An agent can tell exactly what this tool does and what it does not do.

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 explicitly says when to use this tool ('To change the lead's stage use update_stage; to manage tags use add_tag / remove_tag') and provides identification guidance ('Identify the lead by lead_id or phone_number'). It also clarifies partial-update semantics ('Only the fields you provide are changed'), which is critical for correct invocation.

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