List signed-in accounts

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

Annotations already declare readOnlyHint and idempotentHint, lowering the burden. The description adds useful behavioral context beyond that: it reveals the existence of a `valid` flag and the auth workflow required for invalid accounts. It also clarifies the default-account concept. No contradictions or misleading statements.

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 description is compact, front-loaded with the main purpose, and uses three short sentences to cover purpose, cross-tool relevance, and the auth caveat. Every sentence adds necessary information without redundancy or 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?

Given the output schema exists and the annotations cover safety and idempotency, the description supplies the missing cross-tool context and validity/auth semantics. Nothing required to call or interpret the tool correctly is missing, making it complete for this straightforward list operation.

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 has zero parameters, so the schema already fully covers the input contract. Per the 0-param baseline of 4, no additional parameter documentation is needed, and the description appropriately focuses on output-related context instead.

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 verb ('List') and a specific resource ('the Google accounts calendar-mcp can use') plus the additional distinction of which is default. This clearly separates it from the event/calendar-oriented sibling tools, none of which deal with account enumeration.

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?

The statement that every other tool takes an optional `account` argument naming one of these makes the practical use case clear: run this to discover valid account names for subsequent tool calls. It does not explicitly say 'use when you need the default account' or exclude alternatives, but the context is strong and there is no sibling tool serving the same function.

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