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

Annotations cover the safety profile (readOnly, idempotent, non-destructive), and the description adds genuinely non-obvious behavior: the rounding tie-break that returns the larger gross so CIS is never under-deducted, the return shape (forward working, pence and pounds), and the VAT-exclusion caveat. That is meaningful context beyond the structured fields, though it does not discuss limits or errors.

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 sentences, all earning their place, with the core purpose front-loaded and the rounding rule and VAT caveat following. Slightly dense but no filler.

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 no output schema, the description steps in to explain what comes back (forward working, pence and pounds) and flags the rounding determinism and VAT exclusion. For a 3-param read-only calculator that is essentially complete; only explicit routing to the sibling tool is missing.

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 net, materials and rate are already fully documented in the schema, including the 0/20/30 enum meanings. The description adds the framing that net is post-CIS and VAT-exclusive, but no new syntactic or edge-case detail beyond the schema baseline.

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 precise verb+resource: finds the gross amount (excluding VAT) from a given net after the CIS deduction. The title's 'net to gross' and the explicit 'for a subcontractor quoted a take-home figure' clearly distinguish it from the forward-direction sibling cis_deduction.

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?

It gives a clear trigger context (subcontractor quoted a take-home figure, so you need to work backwards), which is exactly the situation that selects this tool over cis_deduction. However, it never explicitly names cis_deduction as the alternative for the forward direction, so the routing is implied rather than stated.

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