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

Annotations already declare readOnly/idempotent/non-destructive, and the description adds real value on top: the product-level default filters and how to bypass them (pass 0), the compact-vs-all filtering behavior, rejection-reason payload on non-qualifying rows, the meta.caps_applied.available uncut-size signal, and the required api:read scope. It stops short of describing snapshot freshness/staleness beyond the word 'materialized'.

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?

Front-loaded with what the tool returns, then defaults, then view semantics — every clause carries information. It is a dense single paragraph, slightly overpacked, but there is no 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?

With no output schema, the description shoulders return-value explanation and does so well (field list plus meta.caps_applied.available). The remaining gap is the three undocumented parameters, which leaves the agent guessing on min_abs_z and session selection.

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 only 33%, and the description restates the two filter defaults already documented in the schema while leaving min_abs_z, limit, and market_session completely unexplained in both places. It compensates partially, not fully, for the coverage gap.

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 (US-equity session movers from the Daily Moves snapshot) and enumerates the returned fields (session return, z-score vs annual distribution, dollar volume, market cap, qualifies_big_move). An agent can tell this apart from get_daily_move_context or get_market_brief without opening a 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?

Gives clear when-to-use guidance for the two modes: view=compact for qualifying movers, view=all 'useful for why is X not listed'. It does not, however, route the agent away from the adjacent daily-move/context/plan siblings, so the alternative-selection guidance is incomplete.

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