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

The key behavioral trait—upserting existing names instead of creating duplicates—is disclosed, which is valuable beyond the sparse annotations (title only). It does not mention side effects like overwriting fields, but the most important nuance is covered.

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 no filler. Every word contributes to explaining purpose and behavior.

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 simple contact-creation tool, the description explains the operation and the key behavioral nuance. It doesn't describe return values or error cases, but given the absence of an output schema and the simplicity, this is acceptable.

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 meaning to the 'name' parameter by explaining that it serves as the deduplication key, which is useful context not present in the 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?

Description uses specific verb 'Save' and identifies the resource 'address book', clearly distinguishing from sibling tools like contacts_find, contacts_list, and contacts_delete. It also clarifies the add/update behavior, making its purpose 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?

The description makes the use case clear—saving someone to the address book—and the upsert caveat implies when to use it (adding a new person or updating an existing one). It does not explicitly name alternative tools or exclusion criteria, but the context is sufficient.

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