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

Goes well beyond the annotations (readOnly, idempotent, closed-world) by adding no-network, no-stored-state, determinism, and concrete operational limits: 64 KB input, 1 s per call, 1 MB result. That is exactly the extra context an agent needs before calling.

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?

Labeled sections (when / not-for / side effects / determinism / limits) are strongly front-loaded and easy to scan. The full Spanish + English duplication doubles the length, which is a real cost, though it is presumably deliberate for a bilingual toolset.

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 single-parameter read-only decoder with an output schema present, nothing needed to invoke it correctly is missing: scope, exclusions, side effects, determinism and resource limits are all stated.

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% with a single required 'ulid' string, so the schema already documents the parameter fully. The description adds output meaning (what gets extracted) rather than parameter meaning, so the baseline 3 applies.

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 (validate a ULID, extract its timestamp and random part) and even names the exact decoded outputs (ms, ISO 8601, hex of the 80-bit random part). It is clearly separable from uuid-inspect, which it names, and from the identifier-family siblings.

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?

Provides explicit 'Cuándo' / 'No para' sections and names uuid-inspect as the contrasting alternative with the exact conditions that select it. The one flaw is the 'when' clause mentioning that an identifier 'has to be generated in this format', which points at ulid-generate, not this decode tool, and no alternative is named for that case.

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