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

Annotations already cover read-only, idempotent and non-destructive traits, so the bar is lower, but the description adds the single most valuable behavioral fact: a nonexistent placeholder renders empty rather than failing, making this a silent-failure trap. It does not fill the remaining gap of whether the list is paginated beyond the default page or how large it typically is.

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 sentences, each with a distinct job: what is in the set, when to call it and why it matters, and what it is not for. The built-in enumeration is long but pays for itself by removing a reason to call the tool at all.

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 one-parameter read tool with full annotation coverage, the description covers purpose, trigger and failure mode well. With no output schema present, it leaves the return shape implicit — the agent must infer it gets field keys/labels rather than, say, rendered values.

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?

Only one parameter (`page`) with 100% schema description coverage, so the schema already explains it fully. The description adds nothing about pagination behaviour or when the agent would need to page, which is the baseline-3 case where the schema does the work.

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 — lists team-defined merge fields — and immediately scopes it by enumerating the built-ins so the agent knows exactly what this set contains versus what it already knows. It also distinguishes the resource from per-lead values, clarifying this is not a lead data tool.

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 an explicit trigger condition: 'Check this before writing copy that uses a {{key}} the user mentions.' It also names the alternative for the adjacent need — per-lead values go through `lead_update`, not here — so the agent is routed away from a plausible misuse.

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