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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the bar is low. The description adds genuinely useful operational context: the upstream source (ASX Investment Products report) and the publication lag ('published a few weeks after month end, so it lags'), which matters for freshness expectations. It stops short of stating pagination or exact return shape.

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-loads the data content, then usage, then the caveat and sibling pointer. Three sentences, each carrying distinct information, with no repetition of the title or annotations.

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 carries the burden of describing return content and does so (AUM by fund, issuer, management fee, plus prior-month total). Coverage boundaries, source and lag are all disclosed, leaving nothing an agent needs before calling it.

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?

The tool takes zero parameters, so there is nothing to document and the baseline is 4. The description correctly implies a no-argument, fixed-scope retrieval.

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?

Names a specific resource (month-end AUM of ASX-quoted spot Bitcoin ETFs), enumerates the covered tickers (VBTC, BTXX, QBTC, IBIT), and states the unit (AUD millions) and returned breakdown (by fund with issuer and management fee). An agent can distinguish it from get_bitcoin_etf_flows without opening any 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?

Explicit when-to-use ('questions about Australian Bitcoin ETFs, their size or fees') and explicit when-not-to-use with a named alternative ('does not cover US-listed ETFs (use get_bitcoin_etf_flows)'). Routing is fully determined.

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