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

Annotations already cover the safety profile (readOnlyHint, idempotentHint, destructiveHint=false, openWorldHint), so the bar is lower. The description still adds real value beyond them by guaranteeing what is withheld from the response: credentials and cryptographic state are never exposed, which is meaningful for an agent deciding whether this call is safe to surface to a user.

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?

A single front-loaded sentence with no filler; the verb and resource come first and the security guarantee is a tight subordinate clause. Nothing could be removed without losing information.

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 no-parameter, read-only listing tool with no output schema, the description covers what it returns (names plus readiness) and what it deliberately omits (credentials, cryptographic state). That is sufficient for an agent to call it correctly without further context.

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 zero parameters and the schema is an empty object with additionalProperties=false, so there is nothing for the description to disambiguate. Baseline of 4 applies; no parameter-level meaning is missing.

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 opens with a specific verb and resource ("List named sessions") and adds the scope detail "and readiness," which tells an agent what kind of data comes back. It is clearly distinct from mutation siblings like session_create and session_close, though it does not explicitly contrast itself with session_observe or session_wait.

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 only implied: an agent can infer this is the discovery/enumeration call to make before observing or waiting on a specific session. There is no explicit statement of when to prefer it over session_observe, nor any stated prerequisites, so the routing decision is left to inference.

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