list_templates

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

Beyond the annotations (readOnlyHint=true, idempotentHint=true, destructiveHint=false), the description adds important traits: 'Requires an API key' states an auth need, 'Reads only; no template is created, edited, or sent' reinforces the safety profile, and 'a template rendered with a missing variable goes out with a visible gap' explains the consequence of missing placeholders. The empty-list note also gives edge-case behavior.

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?

The description is well-structured and front-loaded: the first sentence states the core purpose, the second gives usage context and alternatives, and the third covers safety and edge cases. Each sentence earns its place with no filler or redundancy.

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?

Despite no output schema, the description compensates by explaining what the return includes (variable placeholders), when to use it, what alternatives exist, auth requirements, and the empty-list case. For a simple read-only list tool with three optional params, this is fully complete.

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?

The input schema covers all three parameters with descriptions (100% schema coverage), so the baseline is 3. The description does not add any extra parameter-level semantics beyond what the schema already provides, but it does not need to.

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 clearly states the verb and resource: 'List the saved email templates on the account, with the variable placeholders each one expects.' It also explicitly distinguishes itself from a sibling tool by mentioning 'list_marketplace_items covers third-party ones instead,' ensuring the agent knows exactly which tool fits.

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 explicitly tells the agent when to use the tool: 'Use it to pick a template before composing a send, and to see which variables you must supply.' It also provides an alternative by pointing to list_marketplace_items for third-party templates, and clarifies that an empty list is not an error, giving the agent confidence in handling edge cases.

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