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

Annotations only declare readOnlyHint, so the description carries the rest and does so well: it explains that expires_at is renewal expiry, not access-token expiry, and that API-key calls produce no is_current flag. The authentication wall is disclosed with a recovery path. Missing only operational traits such as ordering, count limits or whether revoked sessions ever appear.

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?

Front-loaded with purpose and scope, then return semantics, then the access gate — a sensible ordering. The ACCESS paragraph is slightly long for what it says, but each sentence (authenticate, then retry; start_login doesn't unlock it) prevents a distinct failure mode.

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?

Zero parameters, an output schema, and readOnly annotations mean the description's remaining job is auth gating and return-field interpretation — both covered. Only minor gaps remain (pagination/result limits, and the loose framing of a session as a "device").

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 no parameters, so the baseline is 4; the description correctly adds no parameter discussion. It does spend words on returned fields (channel, user agent, expires_at, is_current), which is value but belongs to return semantics rather than inputs.

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?

Specific verb plus resource ("List the current user's signed-in devices") with an explicit scope qualifier: every session that can still renew, idle ones included. That qualifier is what separates it from get_session (single) and revoke_auth_session (mutation) among the siblings, without naming them.

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?

"idle ones included" and "every session that can still renew" implicitly define what is and isn't returned, and the ACCESS block gives a concrete precondition plus a negative routing hint ("start_login does NOT open this tool"). It stops short of explicitly contrasting with get_session or revoke_auth_session, so the when-to-use-vs-alternative framing is inferred rather than stated.

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