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

Annotations already declare read-only, idempotent, non-destructive and closed-world, so safety needs no restating. The description adds genuine value by disclosing the shape of the result — an overall mood, the biggest stories, and a per-company score on a defined −10 to +10 scale — which the agent cannot get from annotations. It stops short of saying how many companies are returned or how the response is sized.

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?

One front-loaded sentence that leads with the resource and day scope, then enumerates the payload elements in a parenthetical. The tone-scale gloss is a worthwhile use of space; the only mild cost is a slightly dense single-sentence construction.

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 carries the burden of describing returns and it does so for all three components, including the score scale. For a one-optional-parameter, annotation-covered query tool this is close to complete; only result sizing and ordering are unaddressed.

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?

There is a single optional parameter at 100% schema coverage, with the schema already stating it is an optional YYYY-MM-DD that defaults to the latest day. The description's "latest day (or a given day)" merely echoes that default, adding no new syntax or constraint, so the baseline 3 for fully documented params 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?

States a specific verb-and-resource pairing: news tone for the FTSE 100 on a given day, naming the exact return contents (overall mood, biggest stories, per-company tone scores). The scale is defined inline (−10 clearly bad … +10 clearly good), and the day scope separates it from a weekly-digest sibling.

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 "(or a given day)" together with "latest day" implies the default behavior and implies when to supply a date, which is real guidance. However, it never says when to reach for this rather than the daily-company or weekly-note siblings, and there are no exclusions, so usage must be inferred.

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