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

No annotations are provided, so the description must disclose behavioral traits. However, it only says 'Fill {{variable}} placeholders' without explaining behavior such as whether replacement is global, case-sensitive, or what happens if a variable is missing. The description does not sufficiently inform the agent about side effects or constraints.

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 a single, focused sentence that is concise and front-loaded. It contains no unnecessary words or fluff, making it efficient for an agent to parse.

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?

Given the tool's simplicity, the description is too sparse. It does not mention the return value (the filled string) or provide enough context for safe usage, such as handling of missing variables or special characters. An output schema is missing, so the description should fill that gap but does not.

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 has 0% description coverage, and the description does not adequately compensate. It implies that 'template' should contain '{{variable}}' patterns, but it does not clarify the expected format of the 'variables' object (e.g., key-value mapping) or any constraints on the parameters. The description adds minimal meaning beyond the names.

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 tool's purpose: filling '{{variable}}' placeholders in a template string. It uses a specific verb ('Fill') and resource ('template string'), and the tool is distinct from all siblings, which are unrelated string utilities.

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 description gives an implied usage context (when you need to substitute variables in a template), but it does not provide explicit guidance on when to use or avoid this tool, nor does it mention any alternatives. It is minimally adequate but lacks depth.

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