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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), and the description adds meaningful context beyond them: the explicit non-verification boundary against the GST portal and the assurance that "Nothing is stored". It also previews the decoded output fields, though it says nothing about failure behavior (e.g., what a malformed GSTIN returns).

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?

Four short sentences, front-loaded with the core action, then checks, then output, then scope caveat and a privacy note. Every sentence adds information and nothing is repeated from the schema or annotations.

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 validator with no output schema, the description is nearly self-sufficient: it names the decoded return fields and draws the portal-verification boundary. The only material gap is input format expectations, which neither the schema nor the description supply.

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 description coverage is 0% and the single parameter is documented only as a 1-32 character string, so the description carries the burden. It implies the input is an Indian GSTIN but never states the expected 15-character alphanumeric structure, casing rules, or whether whitespace/hyphens are tolerated.

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 ("Validate and decode an Indian GSTIN") and enumerates exactly which checks run (format, state code, embedded PAN, check character), which cleanly separates it from siblings like validate_pan, validate_gtin and converters_vat_validate.

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 sentence "It does not check the registration on the GST portal" is an explicit scope exclusion that tells an agent when this tool's answer is insufficient, which is real usage guidance. It stops short of naming an alternative for portal verification or telling the agent when to prefer validate_pan for the PAN component, so it falls just short of a 5.

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