base64_decode

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

Without annotations, the description fully discloses behavior: 'Has no side effects', error handling ('Returns ... or an error if the input is not valid Base64'), encoding assumption, and return type. This is comprehensive for the tool's simplicity.

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?

The description is concise at 4 sentences, with the core purpose first, followed by important details and a warning. Every sentence adds necessary information without redundancy.

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?

Given the tool's simplicity (1 param, no output schema), the description is complete. It covers purpose, parameters, behavior, error handling, and limitations. No additional information is needed for correct invocation.

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 100% with a clear description for the single parameter. The description adds value by noting that non-ASCII characters are handled correctly, which is not indicated in 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?

The description explicitly states 'Decode a Base64 string back to UTF-8 text', clearly indicating the verb (decode) and resource (Base64 string to UTF-8 text). It distinguishes from the sibling base64_encode by focusing on the reverse operation.

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 explicit when-to-use: 'Use to recover the original text from a Base64-encoded value.' and when-not-to-use: 'Do NOT use to decode binary data — output is always interpreted as UTF-8 text.' This provides clear guidance on appropriate contexts.

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