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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is covered. The description adds light behavioral context by paraphrasing the needs_contact filter as 'needing reach-out', but does not disclose pagination, ordering, or return shape. 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 filler. The action 'List contacts' is front-loaded, and the filter capabilities are stated in the second sentence. Every word earns its place.

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?

Adequate for a simple read-only list tool with full schema coverage and safety annotations. Gaps: it does not state that omitting all filters returns all contacts, nor mention the favorites_only parameter in prose. Without an output schema, the return shape is not addressed, though 'List contacts' implies a list of contacts.

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% with each parameter already described ('Filter by type' for relationship, 'Only contacts overdue for check-in' for needs_contact, 'Only favorite contacts' for favorites_only). The description adds only a paraphrase of needs_contact and relationship, and omits favorites_only entirely, so it does not meaningfully extend 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?

The description states a clear verb-resource pair ('List contacts') and names two filter modes (relationship type, needing reach-out). It does not explicitly differentiate from sibling list_* tools, but the resource 'contacts' is unambiguous and no sibling list_contacts exists.

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?

Usage is implied by the filter hints: use this when you want a list of contacts, optionally filtered by relationship or needing reach-out. No explicit when-not-to-use or alternatives are given, such as 'search' for finding a specific contact or 'update_contact' for modifying one.

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