apply_template

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

With no annotations, the description carries the full behavioral burden and only partially discharges it: 'return the resulting text' hints at a non-mutating render, but nothing states whether this is read-only, how missing or extra variable names are handled (error vs. leftover placeholders), or whether the template must already exist. These are the key behavioral questions for a template-rendering tool.

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?

A single sentence with zero filler, front-loading the action and ending with the return value. Nothing is wasted or buried.

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?

Two fully documented parameters and no output schema mean the description needn't explain return values, and it does state that rendered text comes back. However, for a nested-object input with no annotations, the silence on variable-mismatch behavior leaves a real gap for correct invocation.

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 both parameters are already documented, giving a baseline of 3. The description adds a small amount of meaning by tying the 'variables' object to the {{placeholder}} syntax, but supplies no format, naming, or completeness rules beyond that.

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 combination ('Fill a template prompt's {{variables}}') and discloses the outcome ('return the resulting text'), which cleanly separates it from the CRUD siblings like get_prompt, add_prompt, and update_prompt. It doesn't explicitly name a sibling it is not, so it stops short of a 5.

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 never says when to reach for this versus get_prompt, which presumably returns the raw unrendered template. An agent must infer that distinction from the verb alone. No prerequisites, exclusions, or alternatives are stated.

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