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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=false, so the agent knows this is a safe, non-destructive, local read operation. The description adds a payment flow (402 response, USDC payment, PAYMENT-SIGNATURE header), which is valuable behavioral context. However, it does not describe output format beyond a brief mention of hunks, nor does it warn about input size limits or rate limits. A 3 is appropriate given annotations cover the safety profile and the payment detail adds some value.

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 starts with the core function, then lists use cases, and finally explains the payment flow. It is front-loaded and each sentence serves a purpose, though the payment details in Japanese are somewhat verbose and could be more concise.

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?

The tool is simple (two string parameters, no output schema). The description explains the return format (added/removed/unified hunks with counts) and the payment requirement, which is unusual and important. It lacks information about maximum input size or error handling, but with annotations covering safety, it is largely 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 description coverage is 100%, so both parameters (a and b) are fully documented in the input schema. The description does not add any parameter syntax or meaning beyond what the schema provides. Baseline 3 is correct when the schema does the heavy lifting.

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 (return), resource (line-level diff between two texts), and output shape (added/removed/unified hunks with counts). It clearly distinguishes this tool from siblings like csv-json and regex, which perform entirely different transformations.

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?

Explicitly lists concrete use cases: reviewing a patch, comparing API responses, and pre-checking whether documents differ to save tokens. This gives the agent clear when-to-use context, and the nature of the tool makes alternatives obvious.

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