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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is covered by structured data. The description adds real value beyond that: the `market` flag signals whether the US session is open, and when closed the moves reflect the last session — critical interpretation context for a snapshot tool. It stops short of describing refresh cadence or how stale the snapshot can be.

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?

Three sentences, front-loaded with what is returned, then the session caveat, then the routing to the sibling tool. No filler, no restatement of the title, and every sentence carries information an agent needs.

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?

There is no output schema, so the description carries the burden of describing the return shape — and it does, enumerating breadth, gainers/losers, segment moves, ETFs and regime. The session-open caveat resolves the main ambiguity in interpreting a 'today' snapshot, so nothing material is missing for a zero-parameter read tool.

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 no parameters, so there is no parameter semantics to document; the schema is an empty object at 100% coverage. The description does usefully clarify the meaning of one returned field (`market` as session-open indicator), which helps interpretation.

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?

Specific verb ('Returns') plus a precisely scoped resource ('today's snapshot of tracked AI and semiconductor companies') with an explicit enumeration of what the snapshot contains: breadth, top gainers/losers, segment moves, reference ETFs, and regime. It also explicitly contrasts itself with the sibling get_market, so an agent can choose correctly without opening any schema.

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?

States the triggering condition plainly ('Use it when the user asks how the sector is doing today') and names the alternative with its distinct condition ('For market cap and volume over time, use get_market'). Both when-to-use and when-to-use-something-else are explicit.

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