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

Annotations already declare readOnly/idempotent/non-destructive, but the description adds real value beyond them: 'Nothing is stored and no receipt is kept' confirms no persistence, the price-source sentences explain the openWorld behavior, and 'A general calculation, not a fatwa' sets the authority boundary. It does not disclose rate limits or failure modes for price lookups.

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?

Front-loaded with verb and resource, then conditions. Dense but every clause carries information (nisab thresholds, price sources, madhhab handling, disclaimer). It is a single long paragraph that could be split for scanability, which keeps it below a 5.

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 7-parameter calculator with full schema coverage and no output schema, the description covers methodology, pricing sources, worn-jewellery handling and the non-fatwa disclaimer. The main gap is that it never says what the result contains (zakat due, nisab status, both-views breakdown), which matters since there is no output schema.

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 goes beyond the schema by explaining the religious and numerical rationale behind parameters: 85 g gold / 595 g silver nisab, 2.5% rate, one hijri year haul, karat-vs-fineness handling, and why worn_jewellery offers multiple views. This meaningfully aids correct parameter selection.

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: 'Work out zakat (zakat al-mal) on a person's gold', immediately distinguishing it from the sibling tools, which are all price lookups, tax, or record verification. The scope (per-person gold zakat calculation) is unambiguous.

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?

Gives clear conditional context for the key branches: Indonesia uses the Antam buyback price, elsewhere the world gold price in the person's currency; worn jewellery is shown both ways unless the person states a madhhab. It does not explicitly route away from siblings or say when not to use it, but the conditional guidance is strong.

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