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

Annotations declare destructiveHint=true and idempotentHint=true, so the agent knows this mutates and overwrites, but the description never explains what 'destructive' means here — whether omitted fields are preserved or cleared, or whether overwriting a custom field loses prior values. The only behavioral content is the schema pointer, which the input schema already states verbatim.

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, front-loaded with the operation and followed by the prerequisite. Nothing is padded, though the second sentence largely restates what the schema property already says, so it is not perfectly economical.

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 destructive mutation with nested custom_fields, an output schema, and full param documentation, the main missing piece is update semantics — partial vs full replacement and the consequences of the destructive flag. The resource pointer is present, but the risk profile an agent needs before writing is not.

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% and the custom_fields parameter description already spells out the 'read crm-schema first, exact field codes, unknown codes rejected' rule. The description's version of that instruction adds nothing new, so this sits at the baseline for a fully documented 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?

States a specific verb and resource ('Update an existing opportunity (deal) in the CRM'), and the '(deal)' gloss clarifies domain vocabulary. It doesn't explicitly contrast with create-opportunity-tool or update-company-tool, but the create/update distinction is unambiguous from the name and verb.

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 custom fields (read the crm-schema resource first), which is actionable guidance. However, there is no statement of when to prefer this over siblings like update-company-tool, or what conditions make an update inappropriate.

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