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

Annotations already establish readOnly, non-destructive, idempotent, closed-world behavior, so the description only needs to add nuance — and it does: UTF-8-safe round-tripping, the ability to read a ULID's embedded timestamp, and the explicit warning that JWT decoding performs no signature verification. Missing are error behavior on malformed input (invalid Base64, bad JWT) and the fact that UUID/ULID generation is random rather than deterministic per call.

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 dense sentence that front-loads the most common uses (Base64/URL) before the more specialized ones (hashes, identifiers, JWT). Every clause corresponds to a real capability, so nothing is filler. It is slightly list-heavy but well ordered for scanning.

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 an eight-operation multiplexer with no output schema and no parameter descriptions, the definition leaves meaningful gaps: which parameters pair with which `op`, what each call returns (a string? an object with header/payload?), and how failures are surfaced. The safety profile is fully covered by annotations, but the operational contract for a multi-mode tool is only partially described.

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?

With 0% schema description coverage and six parameters, the description carries real weight: it names the algorithms behind `algo` (MD5/SHA-1/256/384/512) and the `version` values (v4/v7), and explains the ULID-time case. However, `count`, `url_safe`, and `text` are never addressed, and it does not say which parameters apply to which `op` value (e.g., `algo` only for hash, `url_safe` only for base64), which is the main ambiguity in a multiplexed 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?

The description enumerates every capability with a concrete verb+resource: Base64/URL encode/decode, five named hash algorithms, UUID v4/v7 and ULID generation, ULID time extraction, and JWT header/payload decoding. This maps almost one-to-one onto the `op` enum, so an agent can identify the tool without opening the schema. It stops short of 5 because it does not say how it differs from generic siblings like `convert` or `text`.

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?

Usage is implied by the enumerated operations rather than stated: an agent infers 'use this when you need to hash, encode, or mint an identifier.' The one real routing hint is the caveat that JWT decoding is done 'without verifying it,' which implicitly points at `verify`-style siblings for trust checks. There is no explicit when-not guidance or prerequisite statement.

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