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

It discloses billing behavior (price per call, first 25 free, failed calls free) and explicitly explains the unusual annotation state ('not marked read-only because each call is charged'), which reconciles readOnlyHint=false with a non-destructive compute operation. That is real context beyond what the annotations convey.

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?

Purpose and output format are front-loaded, and the example is compact. The pricing/credits sentence is slightly tangential but still earns its place by justifying the annotation and setting cost expectations.

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?

With no output schema, the description carries the burden of describing results and does so ('each line marked as unchanged, removed or added, with counts'). Inputs, use case, cost, and safety profile are all covered, leaving nothing an agent needs missing.

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%, so the baseline is 3, but the inline example (a=one\ntwo\nthree, b=one\n2\nthree\nfour) concretely demonstrates that the inputs are multiline strings and how they pair up. That adds meaning beyond the terse 'original text'/'new text' schema descriptions.

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 gives a specific verb and resource ('Line-by-line difference between two texts') and even specifies the output shape ('each line marked as unchanged, removed or added, with counts'). This is clearly distinguishable from siblings like text_stats or text_extract, which measure or extract rather than compare.

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?

It states a clear use context ('see what changed between two versions of a document, config or prompt'), which tells the agent when this tool applies. However, it names no alternative tools and gives no when-not-to-use condition, so it stops short of full routing guidance.

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