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

Annotations already indicate non-read-only and non-idempotent behavior; the description adds specific behavioral detail: CSV header requirements, custom field mapping, tag application to all imported contacts, and the return summary object. It does not explain duplicate handling or failure modes, but it goes meaningfully beyond the annotation flags.

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 compact at three sentences, front-loaded with the action, and contains no filler. Every sentence adds useful information about input format, behavior, or output.

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 tool with three parameters and no output schema, the description covers the main input constraints, a core behavioral effect, and the return object shape. The only notable gap is the unexplained 'source' parameter and lack of explicit error/duplicate semantics, but overall the agent has enough to invoke it correctly.

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 67% (csv_data and tag), and the description enriches both: csv_data must contain a header row with required 'phone' and 'name' columns, additional columns become custom fields, and tag is applied uniformly. The 'source' parameter remains undocumented both in schema and description, preventing a 5.

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 states a specific action (bulk import), resource (contacts from CSV string), and key input format. It naturally distinguishes itself from siblings like list_contacts and add_or_update_contact by emphasizing bulk CSV import and the required columns/custom field behavior.

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 phrase 'Bulk import contacts from a CSV string' clearly establishes the intended use case, and the required-columns detail reinforces when this tool is appropriate. It does not explicitly name alternatives or exclusion cases, but the context is strong enough for an agent to choose it over singular add_or_update_contact.

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