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

Annotations only declare it is non-read-only, non-idempotent, non-destructive. The description adds real behavior beyond that: it hosts every image, converts merge tags to Send16 format, and stores HTML exactly as designed. That is meaningful operational context an agent could not infer from structured fields.

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?

Front-loaded with the core purpose, then the trigger, then behavioral notes, then HTML guidance, then the return/follow-up. The email-safe rendering sentence is long but earns its place. Slightly verbose but no filler.

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 8 params, no output schema, and a non-read-only mutation, the description covers return value ('Returns the template id'), the follow-up action, content-fidelity behavior, and HTML quality expectations. Nothing an agent needs to call this correctly is missing.

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 goes further by stressing 'pass the complete email HTML' and describing exactly what happens to HTML content (image hosting, merge-tag conversion, email-safe layout requirements). This adds value beyond the schema's per-parameter descriptions.

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+resource ('Save an email design as a reusable template in the user's Send16 workspace'), clearly distinguishing it from design_email_template, get_template, and list_templates. An agent instantly understands this is a write-into-library operation.

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 a concrete triggering scenario ('when the user has designed an email, for example in a Claude artifact') and a follow-up path (send_template_test). It does not explicitly exclude alternatives like design_email_template, so it stops short of full when/when-not routing, but the context is clear.

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