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

Annotations already confirm readOnly/idempotent/non-destructive, so the bar is lower, and the description adds real behavior: it reads the latest SEC holdings report and screens each holding by industry and debt, and it uses an index-tracking proxy for UK listings. It stops short of stating latency, coverage limits, or what happens on unresolvable tickers.

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?

The opening sentence is front-loaded, but the title is then repeated verbatim as the first sentence, and the final sentence is a dense run-on mixing UK tickers, fund names, and index-proxy behavior. It could be tightened without losing information.

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 single-parameter, no-output-schema lookup, the description gives enough about the resolution logic and data source to call it correctly. Only the unresolvable-input behavior and possible response latency are unaddressed.

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 schema already documents that the ticker accepts a fund/ETF ticker or a Shariah fund name. The description only adds extra UK example tickers (VUSA, CSPX, VWRL), which is marginal value over the schema, so the 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 decision ('is this fund/ETF/pension fund halal') and the resource it operates on, and the screening mechanism (Shariah recognition, SEC holdings, index proxies) makes it clearly distinct from siblings like screen_stock or check_crypto. An agent can pick this over the alternatives without opening the schema.

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 implicitly routes three cases: Shariah funds by name/ticker, other US-registered funds/ETFs via SEC filings, and UK-listed ETFs/names via an equivalent US index fund. That covers when each path applies, but it never states exclusions or explicitly points to the sibling that handles individual equities (screen_stock).

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