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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), so the bar is lower, and the description still adds real behavior: the as_of default of today, that a snapshot is 'the latest on or before' the date, that values are per currency with per-account totals, and that cost basis is only present 'where reported'. It does not mention pagination, auth, or rate limits, but the key data-shape behaviors are disclosed.

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?

Two dense sentences with the core resource and its returned fields front-loaded, followed by snapshot and formatting caveats. The colon-heavy clause structure is slightly awkward but every clause carries information; nothing is wasted.

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 returns, and it does so by enumerating the fields and explaining per-currency/per-account aggregation and the conditional cost basis. It is complete enough for an agent to call and interpret the result, with only minor gaps like no mention of account_id sourcing.

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 goes beyond it by clarifying the as_of default ('default today'), the snapshot semantics, and the decimal-string quantity format for fractional shares. These details help interpret the returned data even though the parameters themselves are already documented 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 names the resource (positions in investment accounts), enumerates the exact fields returned (security/ticker/name, quantity, price, value, cost basis), and explicitly draws the boundary against the sibling list_accounts ('Account balances themselves are in list_accounts'). An agent can distinguish it from get_bucket, get_cap_table, and get_liabilities 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?

Usage is implied rather than stated: it routes account-balance questions to list_accounts and explains the as_of snapshot semantics, which helps an agent decide what the tool is for. But there is no explicit when-to-use framing, no prerequisite (e.g. needing an account_id from list_accounts), and no other alternatives named despite many sibling get_* tools.

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