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

Beyond the readOnlyHint/openWorldHint annotations, the description discloses real behavioral traits: ISIN and CUSIP check digits are validated before the call, ISINs additionally yield the issuer's LEI and legal name from GLEIF, and there is explicit pricing ($0.002 USDC per successful call via x402 on Base/Solana/Arc) with failed calls not charged. This is unusually rich operational context that an agent needs to budget and reason about cost.

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 identifying purpose and returned fields are front-loaded in the first sentence, followed by two short, information-dense sentences on validation/attribution and payment. Slightly long as a single run-on opening clause, but every sentence carries distinct value.

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 an output schema present the description need not restate return values, yet it still lists them for scannability, and it covers validation, sources, and payment model. The only residual gap is that the one-of identifier requirement (zero required params) is left implicit.

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 meaningful semantics the schema does not: that exchange is optional, that ISIN (unlike CUSIP/ticker) unlocks LEI/legal-name enrichment, and implicitly that one of the three identifiers is the actual input despite zero required parameters. It stops short of an explicit one-of constraint.

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 names the exact resource (a security identified by ISIN, CUSIP or ticker), the lookup source (OpenFIGI, with GLEIF enrichment for ISINs) and enumerates the returned fields. It is clearly a securities-identifier resolver rather than a generic search, though it never names or contrasts a specific sibling such as company_ticker or lei.

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?

Usage is implied by the identifier inputs and the note that exchange is optional, but there is no explicit when-to-use / when-not-to-use guidance and no routing to an alternative tool. An agent must infer the trigger condition from the parameter set alone.

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