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

With no annotations, the description carries the burden, and it discloses two meaningful traits: case is preserved and the operation is pure CPU/instant (deterministic, no side effects or external calls). It does not state the return shape, but for a self-inverse text transform that is nearly self-evident.

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 short sentences, zero filler, with the core action and the bidirectional property front-loaded. Every clause earns its place.

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 trivial single-parameter pure function with no output schema, the description covers the essentials an agent needs. Minor gap: it doesn't mention non-alphabetic characters passing through unchanged, which is the one behavior an agent might wonder about.

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?

One parameter with 100% schema description coverage, so the schema already defines 'text'. The description adds no format, length, or character-set constraints beyond 'text to rotate', which is the expected baseline when the schema does the work.

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 (Apply) and a specific resource (ROT13) plus scope ('to text'). ROT13 is a distinct named transform, so an agent can separate it from caesar_cipher/atbash siblings, though the description doesn't name those alternatives.

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?

'in either direction' implicitly tells the agent no separate encode/decode mode exists, which is real usage guidance. However, there is no explicit when-to-use versus sibling ciphers like caesar_cipher or atbash, leaving selection to inference.

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