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

Annotations already cover safety (readOnly, idempotent, non-destructive, open world), so the bar is lower, yet the description adds real context: the ratio comes from the latest 10-K that reports interest income, and 'latest_annual_filing'/'note' signal when that is stale. It also warns that purification does not make an excluded business permissible, a meaningful behavioral caveat.

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?

Three sentences, front-loaded with the core purpose, then the return values, then the caveat. Dense but purposeful; the parenthetical about 'latest_annual_filing' and 'note' is slightly nested but earns its place by explaining staleness.

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?

There is no output schema, so the description carries the burden of explaining returns, and it does: it defines the purification ratio, names the fields indicating data recency, describes the conditional charity amount, and flags the business-screen limitation. Nothing an agent needs to call this correctly 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 coverage is 100%, so baseline is 3, but the description adds meaning beyond the schema by explaining that 'dividend' is optional and changes the output (charity amount is returned only when a dividend is supplied). That conditional coupling of the parameter to the response is not in the schema.

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 pair: it computes a company's purification ratio (interest income over total revenue) and, given a dividend, the charity amount. It also discloses the exact formula and the fallback data source, which clearly separates it from mizan_calculate_zakat and mizan_screen_company.

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 — call it after receiving a dividend to learn the charitable portion — but there is no explicit when-to-use or when-not-to-use statement, and no sibling tool is named as an alternative. The business_screen caveat implies screening happens elsewhere, which is helpful but only indirectly.

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