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

Given annotations only indicate non-read-only and non-destructive, the description adds critical behavioral context: the 200-contact limit, the requirement for at least an email, and the deduplication logic (update vs create). This goes well beyond what annotations alone convey.

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 description is three sentences, front-loaded with the primary action, and every sentence carries essential information (purpose, usage trigger, requirements, limits, behavior). No wasted words.

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 batch operation with a nested contact object, the description covers the key points: batch scope, required field, limit, and upsert semantics. It does not address error handling or partial failures, but with no output schema and given the tool's relative simplicity, it is reasonably complete.

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?

The schema describes the 'contacts' parameter as 'List of contacts to add' (100% coverage), but the description adds vital semantics: each contact must have an email, supports up to 200 contacts, and deduplication behavior. This enriches the raw schema information.

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 opens with a specific verb and resource: 'Add multiple contacts to Xmagnet in one call.' It clearly distinguishes from siblings like create_contact by emphasizing batch operation and the upsert behavior (existing updated, new created).

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?

Provides explicit context: 'Use when user provides a list of contacts to add/import.' This clarifies when to invoke the tool, but it does not explicitly name alternative tools or state when not to use it, so it stops short of the highest bar.

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