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

Annotations already cover read-only, idempotent, non-destructive, closed-world, so the description correctly spends its space on extra traits: no network, no stored state, determinism, and concrete limits (1 s per call, 1 MB result). One weakness: it states 'JSON input up to 64 KB' while the schema allows data of maxLength 1048576 — an agent could be confused about the true input ceiling.

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?

Each language block is tightly front-loaded: purpose, when, not-for, side effects, determinism, limits — zero filler. The same content is, however, delivered twice (ES and EN), roughly doubling token cost for the reader, which is the only thing keeping this off a 5.

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?

With an output schema present, the description need not explain return values, and it still covers side effects, determinism, limits and the alternative tool. For a three-parameter hash function this is everything an agent needs to call it correctly.

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 description coverage is 100% with two enums fully enumerated and defaults stated, so baseline 3 applies. The description's phrase 'text or bytes' only vaguely hints at the utf8/hex/base64 input_encoding choice and adds no syntax or format guidance beyond the schema.

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 and resource ('Computes the SHA-512/256 digest') and immediately disambiguates it as the FIPS 180-4 truncated variant with distinct IVs, not a plain truncation of SHA-512. It also names the sibling hash-sha512 so an agent can separate the two without opening either schema.

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?

Explicit 'When' clause (compare content, match a published checksum) and explicit 'Not for' clause routing to hash-sha512. This is the when/when-not/alternative pattern in full, leaving nothing to inference.

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