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

Annotations cover the safety profile (readOnlyHint=false, destructiveHint=false, idempotentHint=false, openWorldHint=false), so the bar is lower. The description still adds real behavioral content: the note is one-line, and the call may have the side effect of classifying a previously unclassified session — a non-obvious consequence an agent should know.

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?

Two compact sentences, front-loaded with the action and immediately followed by the target scoping and the side-effect caveat. Minimal waste, though the parenthetical scoping phrase interrupts the flow slightly.

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 small mutation tool with annotations covering safety and a schema documenting the two optional params, the description is adequate but leaves gaps: it says nothing about the effect on the session's state beyond classification, failure behavior, or whether the note persists. No output schema exists, so return behavior is also unaddressed.

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 67%: op_id and session_id carry detailed schema descriptions (including the replay/idempotency semantics), so the description only needs to compensate for the undocumented note param. It does so partially by saying "one-line" and clarifying which session is targeted by default, but adds no format or length detail beyond that.

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+resource ("Add a one-line note to a running session") and scopes the target to this connection or a session_id. It is clearly distinguishable from siblings like add_steps or add_session, though it doesn't contrast itself with them explicitly.

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 parenthetical "this connection's, or session_id" implies the default target, which is helpful, but there is no explicit when-to-use/when-not guidance or named alternative among the ~40 sibling tools. Usage is implied rather than stated.

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