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

Annotations already declare readOnlyHint=true, so the safety profile is covered. The description adds that results are scoped to the signed-in user and names the backing endpoint, but says nothing about auth requirements, error behavior, or ordering. Note the POST endpoint is disclosed despite the read-only annotation – this is not a contradiction, since many read operations use POST, but it is worth flagging for an agent that infers semantics from the verb.

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 short sentences: what it returns, how it's used, and the endpoint. Front-loaded with the payload shape and free of filler. Every sentence adds something.

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 return contract and does so adequately by naming account_id and name. For a simple zero-param read tool with a readOnlyHint annotation, only minor things (pagination, empty-result behavior) are unstated.

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?

Zero parameters, so nothing needs explaining beyond the absence of filtering. The description correctly implies no inputs are required. Baseline 4 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 the specific resource and its shape: 'The Rex agency accounts (account_id and name) this user can sign in to.' An agent immediately knows it returns a list of accounts for the authenticated user. No sibling tool lists accounts, so no sibling differentiation is needed, though a leading verb ('List...') would make it crisper.

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?

Gives real operational context: 'A user with several accounts picks one with the Account id field when connecting,' which tells the agent both when this tool is relevant (multi-account users) and what downstream value the result feeds. It stops short of stating prerequisites or what to do when only one account exists.

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