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

Annotations already declare a safe read (readOnlyHint, idempotent, non-destructive), and the description adds substantial behaviour the annotations cannot: the default statuses used when no status field exists, that built-in fields are immutable via the API, how writable built-ins map to other operations (assignLead, listContactNotes), and the warning that custom_fields are not validated against this list.

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 purpose is front-loaded and every clause carries real information (default statuses, built_in semantics, writable-property mapping, validation caveat). It is dense, near-reference-material length for a simple list tool, which slightly hurts scannability but not correctness.

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 carries the return-value burden and does so: it explains that the field keyed 'status' exposes options, the default fallback statuses, and the built_in flag meaning. Combined with annotations covering safety, an agent has everything needed to call and interpret this tool.

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?

There is a single agent_id parameter and the schema description coverage is 100%, with the schema itself documenting the 404/403 error behaviour. The description adds nothing further about parameters, so the baseline 3 for schema-carried semantics applies.

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 agent's lead fields') and immediately scopes it as the lead form in display order, which is the field schema rather than lead records. This clearly separates it from siblings like list_leads and get_lead.

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?

Implied usage is clear: the keys of non-built-in fields are 'what custom_fields is for,' so an agent knows to read this before writing custom field values, and it warns to validate before writing because the API doesn't check. It stops short of naming an explicit alternative or a when-not-to-use condition.

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