cyberchef_xor_key_length

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

Beyond the readOnly and idempotent annotations, the description discloses meaningful behavior: it uses three independent statistics, reports disagreements rather than averaging them away, and decrypts. It also provides measured success rates and known limitations, giving an agent realistic expectations about output quality.

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?

Four dense sentences cover function, methodology, output behavior, differentiation, and limitations without wasted words. The core purpose is front-loaded, and every sentence adds information useful for selecting and invoking the tool.

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 complex crypto-analysis tool with no output schema, the description covers method, output behavior, success rates, and limitations. It could be slightly more explicit about the exact shape of the returned candidates and decrypted preview, but the schema's preview_bytes and candidates parameters plus the description's 'reports what each method concluded' make the behavior sufficiently clear.

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?

The input schema has full, detailed descriptions for all six parameters, including encoding options, defaults, and ranges, so the description does not need to restate them. The description adds little parameter-specific meaning, but baseline 3 is appropriate because the schema already carries the documentation burden.

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 opens with a specific verb and resource: 'Recover the key length of a repeating-key XOR' and explains it also scores key bytes against English and decrypts. It clearly differentiates itself by noting CyberChef's XOR Brute Force stops at a two-byte key, positioning this tool for longer keys.

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?

The description gives useful selection context: CyberChef's XOR Brute Force only handles two-byte keys, implying this tool is for longer repeating-key XOR. It also adds reliability guidance by warning that it is least reliable on short inputs and plaintext with strong periodicity, though it does not explicitly name sibling alternatives or provide a full when-not-to-use list.

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