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

Annotations cover the safety profile (readOnly, idempotent, closed-world), so the bar is lower. The description adds real value beyond them: the returned fields, the UNSUPPORTED_VALUE rejection for other scripts, and the $0.05 x402/USDC-on-Base payment requirement — non-obvious operational context an agent cannot infer.

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?

A single dense paragraph that front-loads the core purpose and standard semantics before returning to outputs and pricing. Every sentence carries information, though the pricing clause is appended abruptly rather than structured.

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 compensates by enumerating the return fields (transliteration, source script, standard, mapped fraction, unmapped characters) and the error path. Limits and enums live in the schema, so the definition is essentially complete 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%, so the baseline is 3, but the description adds semantic meaning the schema does not: ISO 9 is one-to-one with diacritics and full coverage, while BGN/PCGN is Russian-only with pass-through for unmapped characters. That materially clarifies the 'standard' parameter's behavior.

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?

States a specific verb and resource ('Cyrillic transliteration to Latin') and names the two supported standards, distinguishing it from every sibling (none of which do transliteration). The scope — which scripts and letters each standard covers — is explicit.

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 clearly explains how to choose between the two standards: ISO 9:1995 for full Slavic/historic/non-Slavic coverage, BGN/PCGN for Russian only, with non-Russian letters passed through unmapped. It stops short of explicit when-not-to-use guidance, but the tradeoff is well communicated.

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