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

The description adds behavioral context by specifying the input encoding as UTF-8, which is beyond the readOnlyHint annotation. It also explains the intended purpose, but does not detail edge cases or output formatting, keeping it from a 5.

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 two sentences long, with the core action in the first sentence and the use case in the second. No wasted words, and it is front-loaded with the key information.

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 simple encoding tool, the description covers the essential purpose, usage, and input encoding. The schema provides full parameter details and the annotation declares read-only behavior, so no additional context is needed.

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%, so the schema fully documents both parameters. The description does not add extra parameter information, matching the baseline of 3 for high 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 clearly states the tool's function: 'Encode a UTF-8 string to Base64.' It uses a specific verb and resource, and the second sentence adds a use case, distinguishing it from sibling tools like text_base64_decode and dev_url_encode.

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 provides a clear usage context: 'Use for embedding data in URLs or APIs that require Base64.' However, it does not explicitly mention when not to use the tool or name alternatives, so it falls short of the highest bar.

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