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

Annotations already mark this as non-read-only, open-world, non-idempotent, but the description adds real behavior beyond them: it may trigger the account's own lead notifications, valid MX records are required, bad addresses surface as a server error, and the new lead id is returned. That is exactly the side-effect and failure-mode disclosure an agent needs before a write.

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?

Four tight sentences, front-loaded with the WRITE marker and effect, then prerequisites, then field mechanics, then return value. No sentence is filler.

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?

With no output schema, the description supplies the return value ('the new lead id'), the mutation's external side effect, the validation constraint that causes hard failures, and how to address nested `fields`. Nothing needed for a correct call is missing.

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, but the description adds the email MX-record precondition, which the schema does not express, and routes discovery of `fields` keys to idx_get_lead. It complements rather than repeats the schema.

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?

Opens with an explicit verb+resource+scope: 'WRITE: creates a new lead in the IDX Broker account', immediately distinguishing it from idx_update_lead and idx_get_lead in the sibling set. The trailing 'PUT /leads/lead' anchors the operation to a concrete endpoint.

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 'creates a new lead' framing plus the pointer to idx_get_lead for discovering field names gives clear context for the create path. It never explicitly says to use idx_update_lead for existing leads or when not to create a duplicate, so exclusions are left implicit.

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