Apply template

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

Annotations already declare readOnlyHint=false, destructiveHint=false, and openWorldHint=true, so the safety profile is covered. The description adds that 'send' transmits immediately, but says nothing about permissions, failure behavior, or whether preview/draft have side effects. Modest value beyond annotations.

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 tight, front-loaded sentences with no filler. The second sentence partially duplicates the action enum from the schema, which is a small redundancy, but overall the text is efficient.

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 100% schema coverage and annotations covering the safety profile, the description need not re-explain parameters or return values. It covers the three action modes, which is the key behavioral fork. Minor gaps remain around send/draft side effects but are acceptable given the structured data.

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 description coverage is 100%, so the schema already documents account, template, variables, to, and the action enum. The description adds only the 'variable substitution' concept, which is largely redundant with the schema's own variable example. Baseline 3 is correct when the schema does the heavy lifting.

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 ('Apply an email template with variable substitution'), which is clearer than the sibling send_email/save_draft by naming the template mechanism. It does not, however, explicitly contrast itself with those siblings, so an agent still infers the boundary.

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 second sentence explains what each 'action' value does, which is mode-selection guidance. But it largely restates the enum already in the schema and gives no when-to-use-this-tool-vs-alternatives (e.g. apply_template+send vs send_email). Usage is implied, not stated.

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