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

Annotations already cover readOnly/idempotent/non-destructive, so the bar is lower. The description adds useful context beyond them: notes are excluded, the birthday edge-case format is disclosed, and it warns that fields from shared/imported cards are data not instructions — a meaningful prompt-injection caveat not present in the 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?

Front-loaded with the operation and its payload, then provenance, then constraints. Every sentence serves a purpose, though the field enumeration partly overlaps the output schema, making it slightly dense.

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?

An output schema exists, so return values needn't be spelled out, yet the description adds selection-critical scope (notes excluded, injection safety, ID provenance). Complete enough for an agent to invoke correctly; only the explicit alternative routing is slightly thin.

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 single parameter has 0% schema description coverage, so the description must carry the burden. It does by explaining provenance ('`contact_id` comes from search_contacts'), which tells the agent where to obtain a valid value — added meaning the bare 'Contact Id' schema does not provide.

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?

States a specific verb+resource ('Read one contact in full') and enumerates exactly what is returned (name parts, nickname, company, emails, phones, addresses, birthday). This clearly distinguishes it from the sibling search_contacts (single-record read vs. search).

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?

Explicitly routes the agent to the prerequisite: '`contact_id` comes from search_contacts,' and scopes out notes with 'Contact notes are never read' (pointing toward get_note). Clear usage context, though it does not state a when-not condition or name the alternative directly.

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