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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint=false, so the safety profile is covered. The description adds genuine domain behavior beyond that: which slabs are currently in force versus legacy, and that the tax is split as CGST+SGST for local vs IGST for inter-state supply, which shapes what the caller should expect from the result.

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?

Two sentences, front-loaded with the core action and rate facts; the trailing web page URL is a mild reference overhead but not disruptive. No redundancy or filler beyond that link.

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 calculator with no output schema, the description supplies the essential context an agent needs: currency-agnostic input, current vs legacy rate application, and the local/inter-state split. Only the shape of the returned breakdown 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 real meaning over the terse schema labels: it explains that 5/18/40 are current slabs and 12/28 are legacy, and ties supply mode to the CGST+SGST vs IGST decomposition. It does omit the 3% enum value present in the schema, which is a minor gap.

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 states a specific verb pair (add/remove) and resource (GST), plus the rate slabs and split rules, so the agent immediately knows this computes Indian GST. It does not explicitly differentiate itself from near siblings such as vat_calculator or sales_tax_calculator, leaving that inference to the agent.

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 mention of modes (add vs remove), supply type (intra vs inter) and the September 2025 slab change, which suggests when each rate applies. There is no explicit when-to-use statement, no exclusions, and no named alternative tool for adjacent tax calculations.

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