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

Annotations already declare destructiveHint=true and readOnlyHint=false, so the safety profile is covered. The description earns additional credit by disclosing that the document operation fully replaces the existing email body and by adding the built-in immutability rule, neither of which appears in the annotations. It stops short of stating permission requirements or whether partial updates are allowed.

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 sentences, no filler, and the mutable-field list is front-loaded ahead of the restriction. Every clause carries a distinct fact an agent needs.

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 5-parameter mutation tool with no output schema, the description covers the main risks: what can be changed, what 'document' replacement means, and that built-ins are excluded. It omits whether at least one field must be supplied and what the response contains, which is a minor gap given annotations and the schema carry the rest.

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 low (40%), so the description must compensate, and it does: it maps name, description, category, and document to their effects, and clarifies that document 'replaces' the body rather than merging. templateId's meaning comes from the schema (list_email_templates). It does not explain accepted category values or length limits, which the schema handles for category but not the others.

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 description uses specific verbs (renames, changes, replaces) against a specific resource (saved template), enumerating exactly which fields are mutable. It also scopes the tool to 'saved' templates versus built-ins, distinguishing it from create_email_template, delete_email_template, and get_email_template without opening their schemas.

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 supplies a clear when-not constraint ('Built-in templates can't be changed'), which is genuinely useful routing information. However, it never names an alternative for the disallowed case (e.g. use_email_template for built-ins, or create_email_template to duplicate one), so usage guidance is implied rather than explicit.

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