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

The description adds genuine scope context beyond the annotations: the field is account-wide and does not touch individual lead values. What it omits matters given idempotentHint=false — it never says what happens if the same key is added twice (error, overwrite, duplicate), which is the main behavioral risk for a non-idempotent create.

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?

Four short sentences, front-loaded with the definition and followed by rationale, sibling routing, and a caveat. Nothing is padded, but the final sentence is wasted space because the fact it asserts is incorrect.

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 two-parameter create with no output schema, the description covers purpose, scope, and the sibling boundary well. It leaves two gaps an agent needs: what the call returns (the created field? just an ack?) and how re-adding an existing key behaves, both amplified by the non-idempotent annotation.

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 earns more by explaining the interpolation syntax ({{key}}) and the resolution rule that the default only fires when a lead has no value of its own. That gives the `value` parameter a purpose and consequence the schema's one-line "Fallback value" does not.

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 opening sentence states a specific verb and resource (define a merge field) plus its operational form (usable as {{key}} in campaign copy). It goes further and distinguishes the tool from `lead_update`, which sets a lead's value, so an agent can tell the two apart 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?

It gives a clear when-to-use signal (defining account-wide tokens for copy) and an explicit not-this alternative (`lead_update` when you want to set a lead's value). However, the closing claim that "There is no tool to delete a placeholder" is factually wrong — `placeholder_delete` and `placeholder_list` are both siblings — which actively misroutes the agent away from the correct tool chain.

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