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

Annotations already establish readOnly/openWorld/idempotent/non-destructive safety, and the description adds meaningful behavioral context beyond them: only finished sessions are listed, today's session appears only after the close, the call returns total count and coverage span, and there is a max of 50 days per call. No contradiction with annotations.

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?

The description is compact and front-loaded: the first sentence states the core purpose and result, followed by relationship to siblings, usage guidance, exclusions, and limits. Every sentence earns its place with no repetition or filler.

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 listing tool with one optional parameter, rich annotations, and an output schema, the description covers purpose, usage boundaries, alternatives, data freshness, archive span, and call limits. Nothing needed to decide when and how to invoke it is missing.

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 schema already documents the single optional 'limit' parameter with default and maximum, and schema coverage is 100%. The description reinforces the max 50 days per call but does not add semantic meaning beyond what the schema provides, so the baseline of 3 applies.

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 states a specific verb ('List'), a specific resource ('finished SPX trading sessions'), and ordering ('newest first'), plus what the result includes (total count, coverage span). It also distinguishes itself from siblings by naming get_session / get_levels as the tools for fetching individual days.

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?

Explicit 'Use when' and 'Not for' guidance is provided: use it to know which days exist or the archive size/span, not for any measurement about a day, in which case get_session is the named alternative. This fully routes an agent to the correct tool.

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