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

Annotations already declare readOnlyHint/openWorldHint/idempotentHint, so the safety profile is covered. The description adds real value by disclosing the algorithm and key-derivation scheme and the structure of the encrypt output (salt, IV, ciphertext). However, it omits behaviorally important facts: encrypt output is non-deterministic (fresh salt/IV), and decrypt fails with an authentication error on a wrong passphrase or tampered bundle.

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 tight sentences with no filler; the algorithm/scope statement comes first and the round-trip contract second. Every clause carries information the agent cannot get from the name alone.

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?

An output schema exists, so return shape need not be explained, and the annotations cover safety. For a 5-parameter cryptographic tool at 40% schema coverage, though, the definition should say how mode selects between text and bundle, what iterations trades off, and what a failed decrypt looks like; those gaps leave it adequate but not complete.

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 only 40%, so the description partially compensates by implying the passphrase (via PBKDF2 key derivation) and the bundle contents (salt, IV, ciphertext). It still says nothing about the 'mode' enum, the 'iterations' knob (default 100000, range 10000-2000000) or the text-vs-bundle exclusivity, leaving meaningful gaps.

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 precise verb pair (encrypt/decrypt) and the exact primitives used (AES-256-GCM, PBKDF2-SHA256), which cleanly separates it from hashing siblings like hash_data/hash_password and encoding siblings like base64_codec. It stops short of explicitly routing against those alternatives, so it is clear but not full sibling differentiation.

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 only implied: 'Encrypt returns a base64 bundle...; decrypt reverses it' tells the agent the two modes exist and roughly what each produces, but never states when to choose this tool over hash_data, base64_codec, or generate_keypair, nor when not to use it. No prerequisites or security caveats are given.

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