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

Annotations already declare readOnly, idempotent, non-destructive, and closed-world, so the safety profile is covered. The description adds genuinely useful behavior: results are scoped to the authenticated user and amounts are expressed in the home currency given by `currency`, which the annotations do not convey.

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 tight sentences that front-load the metric list, then the currency detail, then the sibling hand-off. Every sentence carries distinct information with no filler.

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 compensates by enumerating the returned metrics and breakdown dimension and clarifying currency semantics — enough for correct invocation. The only missing piece is disambiguation from get_portfolio_history.

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 the baseline is 4. There are no inputs whose meaning the description could clarify, and the description correctly implies no filtering arguments are needed.

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?

State a specific verb+resource ('Portfolio-wide metrics for the authenticated user') and enumerates the exact metrics returned (current value, invested, realized, MOIC, DPI, IRR) plus the by_type breakdown. It clearly distinguishes this aggregate view from the per-company listing it routes to via list_companies.

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 provides a concrete routing rule: 'Use list_companies for the per-company rows,' which tells the agent when to prefer the sibling. However, it does not distinguish this tool from get_portfolio_history, another close sibling, leaving one ambiguity for the caller.

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