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

Annotations already declare read-only, idempotent, non-destructive and open-world, so the safety profile is covered. The description goes beyond them by disclosing quota (10 calls/day), per-call pricing, and the two payment mechanisms (params._meta['x402/payment'] or X-API-Key credits) — details an agent genuinely needs before calling. It also notes the output is a 'compact summary', though the output schema already carries return shape.

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?

Front-loaded with the core action, then matching rules, then cost/payment, then provenance. Every sentence carries distinct information; nothing repeats the schema or annotations. The pricing clause is long but each element (quota, price, payment channel) is load-bearing.

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 four-parameter, read-only diff tool with a full output schema, the description covers action, matching semantics, cost model and payment path. Nothing an agent needs before invoking is missing; return-value detail is correctly delegated to the output schema.

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 description adds real meaning: it explains how `key` changes the matching algorithm and what happens when it is omitted (fallback to row index). This behavioral linkage between the parameter and diff semantics is not deducible from the schema's 'key column(s), comma list' alone. `delimiter` auto-detection is left to 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 opening sentence gives a specific verb and resource — 'Diff two CSV strings' — and enumerates the output classes (added/removed/changed rows). The CSV row-level scope implicitly separates it from text_diff and json_diff, though no sibling is named explicitly, so it is clear but not maximally differentiated.

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 explains the matching strategy conditionally: key column when present, key= to override, otherwise row index. That is useful operational guidance, but it never states when to prefer this over text_diff/json_diff or any exclusions/limitations (e.g., CSV size limits, malformed input behavior).

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