decode_isin

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

Annotations already mark the tool as read-only and idempotent, and the description adds meaningful behavioral context: it performs a Luhn check and returns country, NSIN, security type, and Luhn validation. It does not describe behavior on invalid or malformed ISINs, but for a simple read-only decoder this is a minor gap.

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 is compact and well-structured with a summary line, a usage line, an args section, and a returns section. There is no filler, and the most important information is front-loaded.

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 single-parameter read-only tool with an output schema, the description provides all necessary selection and invocation information. It names the scope, the key validation behavior, and the returned fields, making it complete enough for an agent to call it correctly.

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?

The input schema already documents the single 'isin' parameter fully with a 100% schema description coverage and an example. The description only restates '12-character ISIN' without adding new semantics, so the schema carries the explanatory burden.

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 clearly states the operation with a specific verb ('Decode ISIN') and expands the abbreviation to International Securities Identification Number. It adds 'with Luhn check,' making the purpose distinct from other validation and decoding tools for PAN, GSTIN, state codes, and Aadhaar. The tool is easy to tell apart from siblings without opening the schema.

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 explicitly says to use it when validating ISINs, specifically for Indian securities. It gives a clear usage context but does not explicitly name alternatives or state when not to use the tool, so a small amount of inference about sibling decoders/validators remains.

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