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

Annotations already declare readOnlyHint=true, idempotentHint=true and destructiveHint=false, so the safety profile is covered. The description still adds real behavioral context: it confirms no template is applied and explains the confirm-on-apply semantics for previewed values, which annotations cannot express. It does not discuss rate limits or auth requirements, so it is not fully exhaustive.

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?

Three compact sentences with the resource and endpoint front-loaded, followed by the read-only note and the apply_template caveat. The final sentence ('Preview values still need user confirm on apply_template') is slightly awkward in phrasing but carries necessary information, so no sentence is wasted.

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 zero-parameter read tool with an output schema present, the description supplies everything needed: endpoint, scope (authenticated user), keying scheme, side-effect status, and the relationship to apply_template. Return-value details are correctly left to the output schema.

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 tool takes zero parameters, so the baseline is 4. The description usefully explains what the response is keyed by (variable name) and gives example keys, adding orientation that the empty schema cannot 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 and resource ('Return saved template contact field values for the authenticated user') plus the underlying endpoint, and clarifies the keying by variable name with concrete examples (email_address, phone_number). It also distinguishes itself from a write path by noting it is read-only and does not apply a template, so an agent can tell it apart from apply_template without opening either schema.

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?

Gives clear context for use — fetch the stored contact values for the current user — and explicitly frames the boundary with apply_template ('Read-only - does not apply a template') and the follow-on step that preview values still need user confirmation on apply_template. It stops short of naming other get_user_* siblings as alternatives, but the when-to-use condition is unambiguous.

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