Set the default account

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

Annotations already declare readOnly=false, idempotent=true, destructive=false, so safety is covered. The description adds genuinely useful behavior — that the setting only applies to calls that omit an account — but does not say whether it persists across sessions, whether it replaces a prior default, or what happens if the account is not connected.

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?

One sentence, zero filler, with the conditional effect ('when a tool call does not name one') front-loaded so the agent immediately understands the consequence of calling it.

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 setter with annotations covering safety and idempotency, the description covers purpose and effect adequately. It omits the connect-first prerequisite and error behavior for an unknown account, which are the remaining gaps an agent would want.

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 parameter is documented as '@username or Instagram user ID.' The description adds no format, validation, or resolution detail beyond 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?

States a specific verb (choose) and resource (connected account) plus the exact semantic effect: the account used when a tool call omits one. That effect distinguishes it implicitly from connect_account and list_accounts, though no sibling is named.

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 by the purpose statement — call it to establish a fallback account — but there is no explicit when-to-use/when-not guidance, no mention that the account must already be connected, and no routing to alternatives like connect_account for unconnected accounts.

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