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

Annotations already declare a safe, idempotent, open-world read, so the bar is lower, and the description adds real behavioral value by disclosing how the verdict is produced: it reads the latest SEC holdings report and screens each holding by industry and debt. It further explains that UK-listed ETFs are answered via a US fund tracking the same index or the index's constituents, plus UK Shariah options.

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 and dense, but the first two sentences ('Halal or Not. Is this fund… halal?') duplicate the title without adding information. The remaining sentences are tightly packed with mechanism and coverage details and earn their place.

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 one-parameter tool with no output schema, the description covers asset-class scope, recognized identifier types and the screening mechanism well. It does not indicate the shape of the answer (verdict vs. per-holding breakdown) or how ambiguous tickers are resolved, which is a minor remaining 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 coverage is 100% and the single ticker parameter is fully documented, so the schema already carries the load. The description adds marginal value by listing accepted UK tickers and fund names (VUSA, CSPX, VWRL, Vanguard S&P 500, LifeStrategy), which expands the accepted-input surface slightly beyond the schema's VOO/QQQ/SPUS examples.

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 and resource: it determines whether a fund, ETF or pension fund is halal, and it distinguishes scope from the nearby halalornot_screen_stock and halalornot_check_crypto siblings by naming asset classes. The opening two sentences largely restate the title, but the mechanism sentences make the purpose concrete.

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 rather than stated: an agent can infer this is for funds/ETFs/pension funds while screen_stock covers individual equities, but there is no explicit 'use this when / not when' or named alternative. It also doesn't explain what to do for a non-US, non-UK fund.

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