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

Annotations already declare readOnlyHint=false, destructiveHint=false, idempotentHint=false and openWorldHint=false, so the safety profile is known. The description adds a useful behavioral warning that unknown field codes are rejected, but that same warning is already in the schema's custom_fields description, so the added value beyond structured fields is modest.

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?

Two short sentences with the core action front-loaded and the dependency second. No filler or repetition.

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 an output schema present, annotations covering the write semantics, and full schema coverage, the description does not need to explain return values. It is nearly complete, though it could briefly state whether company/contact associations are validated or optional, since only name is required.

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 all four parameters, including the nested custom_fields object and its field-code formatting rule, are fully documented in the schema. The description adds no syntax, defaults, or constraints beyond restating the schema dependency, so the baseline 3 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?

The description gives a specific verb plus resource ("Create a new opportunity (deal)"), which distinguishes it by resource from siblings like create-company-tool and create-people-tool. It stops short of explicitly naming an alternative operation such as update-opportunity-tool, so it is clear but not maximally differentiated.

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 second sentence gives a real prerequisite for the custom_fields path (read crm-schema first), which implies when that parameter matters. However, there is no guidance on when to use this versus update-opportunity-tool or how to handle existing deals, leaving the core when-to-use decision implicit.

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