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

The annotations already disclose that this is a non-read-only, destructive, idempotent operation. The description adds useful behavioral detail beyond that: given values replace stored values, only changed fields should be passed, and field names come from idx_get_lead. It does not cover permissions, error behavior, or response semantics, but it meaningfully supplements 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?

The description is front-loaded with 'WRITE' and then efficiently covers replacement semantics, minimal-field guidance, naming source, and endpoint. Every clause carries actionable meaning with no 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?

For a two-parameter mutation with a nested fields object and no output schema, the description supplies the key operational details: existing lead, replacement behavior, minimal field passing, and field-name source. It could be stronger by explicitly stating that omitted fields remain unchanged and by mentioning response or error behavior, but it is largely complete.

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 adds real value by explaining that field keys are IDX lead field names as returned by idx_get_lead and by giving examples such as firstName, lastName, email, phone, and status, which clarifies the nested fields object beyond the schema's minimal wording.

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 and resource: updates fields of an existing lead. It clearly distinguishes the operation from creation by specifying 'existing lead' and 'WRITE', so an agent can identify it without opening sibling schemas.

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?

It gives clear usage context by saying to update an existing lead and to 'only pass what must change', which helps avoid unnecessary overwrites. It also points to idx_get_lead for field names, though it does not explicitly name alternatives or when-not-to-use cases.

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