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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=false, so safety is covered. The description adds genuine behavioral context beyond that: results are aggregated per source and event data is bounded to the last 7 days, which constrains how the agent should interpret and cache the output.

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?

A single front-loaded sentence that conveys the resource, the grouping dimension (source), the fields returned, and the time window, with no filler or repetition of the title.

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?

With no output schema, the description carries the burden of explaining returns and does so by enumerating the returned categories, which is enough to call and interpret the tool. It stops short of stating result shape or ordering, a minor gap for a zero-parameter read-only listing.

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, and the schema is a closed empty object, so there is nothing for the description to disambiguate. Baseline 4 applies; the description correctly implies the call is unconditional with no filtering input.

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 gives a precise verb+resource ('list every contact field') and enumerates the exact payload: source, type, merge tag, contact counts, company fields, and 7-day events. That scope clearly separates it from mutating neighbors like define_field and unlock_field, though no sibling is named explicitly.

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 only implied: an agent would call this to discover what fields exist before creating segments, defining fields, or filtering contacts. There is no explicit when-to-use, prerequisite, or 'use X instead' guidance, and no exclusions.

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