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

The annotations already declare readOnlyHint, openWorldHint=false, idempotentHint and destructiveHint=false, so 'side effects: none' and 'deterministic' partly restate structured data. However, the description adds genuinely non-derivable operational limits (64 KB JSON input, 1 s per call, 1 MB result) and clarifies the 'no stored state / no network' contract, which is real added context.

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 structure is excellent — front-loaded definition followed by labeled sections (Cuándo / No para / Efectos secundarios / Determinista / Límites). But the entire content is duplicated verbatim in Spanish and English, roughly doubling length without adding information for a single caller.

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?

Purpose, exclusions, side-effect profile, determinism and hard limits are all covered, and an output schema exists so return values need not be described. Nothing an agent needs to call this correctly is missing.

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 the baseline would be 3; the description earns above baseline because 'or any Caesar shift' explains why a 'shift' 1-25 parameter exists and that unchanged defaults give classic ROT13. Minor inconsistency: description cites a 64 KB JSON input cap while the schema advertises maxLength 1048576.

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 names a specific verb and resource ('Applies ROT13 (or any Caesar shift of ASCII letters) to text') and explicitly bounds it against encryption ('Reversible obfuscation only; not encryption'). It also correctly handles the fact that the tool is a general Caesar shift, not just shift-13, matching the sibling landscape of encoders/decoders.

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 contains an explicit 'When:' clause (exact conversion to/from this encoding, no guessing) and an explicit 'Not for:' exclusion that names a concrete sibling, morse-encode. An agent has all the information it needs to route correctly against ~300 siblings.

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