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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=false, so the agent knows this is a safe, side-effect-free local computation. The description adds the useful note that custom rates are permitted, but says nothing about rounding/precision, currency, or validation behavior beyond the enum already in the schema.

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 short sentences with zero filler, and the primary capability is front-loaded before the secondary note about custom rates. Nothing needs trimming.

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?

An output schema exists, so return values need not be described, and the annotations carry the safety profile. For a trivial three-parameter computation this is nearly complete; only precision/rounding conventions are unaddressed, which is a minor gap.

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 100%, so all three parameters (mode, amount, gst_rate) are already documented, including the base-vs-inclusive interpretation of amount. The description's phrase 'custom rates allowed' only restates the gst_rate parameter, adding no new semantics; baseline 3 applies.

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 a specific operation (adding or removing GST) on a specific resource (a monetary amount), and states both directions of the calculation plus custom-rate support. It is clearly distinguishable from siblings such as calculator_percentage or calculator_discount by domain, though it never explicitly contrasts itself with them.

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 two modes imply when each applies (add for base amounts, remove for tax-inclusive amounts), but there is no explicit when-to-use guidance, no exclusion of near-neighbor tools like calculator_percentage or calculator_discount, and no statement of assumptions about rounding or currency.

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