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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered. The description adds useful context beyond the annotations: the data is current, static, and no lookup is performed, which tells the agent this will not hit an external service or change over time.

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 a single dense sentence that front-loads the core subject ('current Companies House late-filing penalty bands') and then efficiently enumerates the covered scope and rules. Every clause adds information; 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?

For a zero-parameter static reference tool with read-only annotations, the description fully covers what the agent needs to select and invoke it correctly. The absence of an output schema is not a gap because the description already communicates the content domain and static nature.

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 input schema has zero parameters and schema description coverage is 100%, so there is nothing for the description to document. The baseline of 4 applies because the description correctly signals a no-input reference tool.

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 names a specific resource (Companies House late-filing penalty bands) and the exact scope (private companies, public companies/plc), plus the two penalty sub-rules covered. The 'Static reference — no lookup performed' clause clearly distinguishes it from a lookup tool like check_company_deadlines.

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 description makes the usage context clear: this is a static reference for penalty bands, not a lookup tool. It does not explicitly name check_company_deadlines as the alternative for deadline-specific queries, but the static-reference phrasing effectively rules out misuse as a lookup.

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