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

With no annotations, the description carries the full burden, and it does add real behavioral content: it discloses that results are ordered/filtered by publication date and that each row also carries the balance sheet date, clarifying the shape of a return value with no output schema. It stops short of stating ordering guarantees, pagination/total-count behavior, or auth requirements, which keeps it from a 5.

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 tight sentences with the core behavior front-loaded and the qualifier about publication vs. balance sheet date immediately following. The trailing use-case sentence is short and adds orientation without padding.

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 2-parameter read tool with no output schema and no annotations, the definition covers the core purpose and one returned field, but an agent still cannot know the full row shape (company name/number, accounts type), result ordering, or whether a total count is returned. Adequate but with clear gaps given the absence of structured output documentation.

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 100%: both parameters ('days' and 'limit') are documented with defaults and min/max bounds. The description's 'last N days' merely restates the 'days' parameter and adds no syntax, format, or edge-case detail beyond the schema, so the baseline 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 gives a specific verb ('List'), a precise resource ('companies whose iXBRL accounts were published at Companies House'), and a scoping filter ('in the last N days'). The parenthetical clarifies that filtering is by publication date rather than balance sheet date, which is exactly the distinction an agent needs to avoid confusing this with a general company search or a balance-sheet-date lookup.

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?

It offers a use-case hint ('useful for monitoring a watchlist or finding fresh signal'), which implies when the tool is appropriate. However, it never names an alternative (e.g. search_companies, find_triggers, watch_list) or states when NOT to use it, so routing between this and its many siblings is left to inference.

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