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

Annotations already declare this is a non-read, non-idempotent, non-destructive mutation, so the safety profile is covered. The description usefully adds a non-obvious side effect ("May classify a session that was unclassified"), which is real value beyond the annotations, but omits error/failure behavior when no running session exists.

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 short clauses with no filler, and the primary action plus target are front-loaded. The parenthetical is slightly awkward but still earns its place by disambiguating the session target.

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 simple 2-parameter tool with no output schema, the description covers target and side effect but leaves a meaningful operational gap: behavior when no session is running, and any note-length/format constraints. Adequate but not complete.

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 description coverage is 0%, so the schema documents nothing. The description compensates for session_id by explaining the default target, but adds nothing about the required 'note' parameter beyond "one-line," leaving its format/length constraints undocumented.

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") and scopes the target ("a running session (this connection's, or session_id)"). It is distinguishable from siblings like add_session or record_progress, though it does not name any sibling 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 establishes which session is targeted by default, which implies usage. But there is no when-to-use vs alternatives guidance and no statement of what happens if no session is running — the description leaves the caller to infer that requirement.

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