Encrypt or decrypt text using the Vigenère polyalphabetic cipher with a letters-only key; set decrypt to true to reverse encryption.
Encrypt or decrypt text using the Vigenere polyalphabetic cipher.
| Name | Required | Description | Default |
|---|---|---|---|
| key | Yes | Cipher key (letters only). | |
| text | Yes | Text to process. | |
| decrypt | No | Decrypt instead of encrypt (default false). |
Changes observed during successful MCP inspections.
v0.1.11Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations are provided, so the description carries the full behavioral burden. It says nothing about case handling, how non-letter characters in the text are treated, or what the tool returns (ciphertext vs plaintext). For a pure text-transform function the risk is low, but the description still omits everything beyond the one-line summary.
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, front-loaded sentence with no filler or repetition. It is efficient, though its brevity is also the reason behavioral detail is absent rather than a sign of discipline.
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 3-parameter, no-annotation, no-output-schema tool, the description is minimal but sufficient to invoke correctly, since required/optional inputs are clear from the schema. It omits the return-value expectation and any edge-case behavior, which would have been worth one more clause.
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 'key', 'text', and 'decrypt' all documented inline, so the schema does the heavy lifting. The description adds no syntax, format, or constraint detail beyond what the schema already states (e.g., letters-only key). Baseline 3 is appropriate given the coverage.
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 states a specific verb pair (encrypt/decrypt) and a specific resource (Vigenere polyalphabetic cipher), so the agent immediately knows what operation is performed. It does not differentiate itself from adjacent cipher siblings such as atbash_process, rot13_convert, or railfence_process, but the cipher name is distinctive enough on its own.
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?
There is no guidance on when to choose this tool versus the other cipher tools in the same family (atbash, rot13, railfence, morse), nor any statement of prerequisites or exclusions. The description is purely declarative and leaves tool selection entirely to the agent's inference from the name.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.