sketch

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

With no annotations, the description must carry the behavioral load. It does disclose a genuine output guarantee (verbatim passages, always includes the opening ask and last word) and the hard constraint of no query, but it does not state that this is a non-mutating read, nor describe pagination, ordering, or failure behavior for an unknown session id.

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 dense sentences, front-loaded with what the caller receives before the scoping caveats. The opening clause ('what one session was about, worked on, and ended up at') is slightly convoluted but every clause carries information; nothing pads.

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 6-parameter read tool with no output schema, the description plus the very detailed schema fields cover cost/breadth limits, windowing for long sessions, and what the returned passages look like. What's missing is modest: no statement of read-only safety and no mention of error behavior on a bad session id.

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 100% and the parameter descriptions are unusually rich (defaults, maxima, the windowing advice, the narrowing report), so the schema does the heavy lifting. The description adds only the `session_id` meaning and the 'no query' absence; baseline 3 is appropriate.

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 names a concrete resource and result shape — 'the passages most distinctive within it, verbatim, always including its opening ask and its last word' — so an agent knows this returns a session digest, not a search hit. It excludes the search use case ('there is no query', 'not a way to find a particular thing in it'), which separates it from recall/scan, though it never names the sibling to use instead.

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?

Clear when-to-use ('enough to tell the user what a session was, in one call') and an explicit when-not ('not a way to find a particular thing in it'), plus the schema's `from`/`to` docs steer long sessions to windowed digests. It stops short of naming which sibling handles the lookup case, leaving that inference to the agent.

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