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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=true, so safety is covered. The description adds one genuinely useful behavioral fact — omitting dates returns the entire history — but says nothing about payload size, pagination, or gaps for days with no data, which matters for a full-history read.

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 compact sentences that lead with the return shape, then the optional-date behavior, plus a short endpoint suffix. No filler and no repetition of schema or annotation content.

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 does carry the burden of describing returns and it does so at a useful level of detail (per-day totals and deltas). For a simple 3-parameter read tool it is nearly complete; only the response envelope (series shape, empty days) is unspecified.

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%, so the baseline is 3, but the description adds meaning the schema lacks: that start_date and end_date are optional and omitting both yields whole-history results, and that the range is inclusive daily granularity. It does not clarify timezone or inclusive/exclusive end-date semantics.

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 the resource (list growth), the granularity (daily), and exactly what is returned (total contacts per day plus daily delta), which distinguishes it from count-style siblings like get_list_contact_counts. It does not explicitly name an alternative sibling, keeping it just below a 5.

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 only usage guidance is 'Omit the dates for the whole history,' which tells the agent how to call it but not when to prefer it over get_list_contact_counts, get_list, or segment-based stats. Nothing is misleading, but the routing between alternatives is left to inference.

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