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

The annotations already declare readOnlyHint=false and destructiveHint=true, so the safety profile is known. The description adds meaningful patch semantics (unspecified fields are preserved), which actually softens the destructive framing, but it omits what happens on an invalid resource_name, whether existing values are overwritten irrecoverably, and any permission requirements. No contradiction with 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?

Two short sentences with zero waste; the mutation intent is front-loaded and the partial-update rule follows immediately. Nothing is padded or repeated.

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 an 8-parameter mutation tool with no output schema and destructive annotations, the description covers the core semantic (partial update) but leaves out prerequisites such as sourcing resource_name and the consequences of overwriting existing contact data. Adequate but not complete for a write operation.

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 every field is documented inline, so the baseline is 3. The sentence "Only provided fields are changed" does add patch-versus-replace meaning that the per-field "Updated ..." descriptions do not convey, but it gives no syntax or format detail for values such as resource_name beyond what the schema already supplies.

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?

"Update an existing contact" gives a specific verb plus resource, and the sibling naming (contacts_create, contacts_delete, contacts_get) makes the operation distinguishable without opening the schema. It stops short of explicitly contrasting itself with those siblings, but the intent is unambiguous.

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?

"Only provided fields are changed" implies this is the tool for partial edits rather than a replace-style write, which is useful guidance. However, there is no explicit statement of when to prefer this over contacts_create or how to obtain the required resource_name (likely via contacts_search/contacts_list).

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