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

Annotations already cover safety (readOnly, idempotent, non-destructive), and the description adds substantive context beyond them: a cost limit ('1 unit'), the critical invariant that 'a gap is never reported as no change', and the fact that gaps and uncertainty are part of the response. These are exactly the operational caveats an agent needs before trusting the result.

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?

Uses a labeled structure (purpose, use cases, Inputs/Returns/Limits) that front-loads the action and keeps each block tight. The opening sentence is slightly overloaded with the record-type enumeration, and the Returns block partly duplicates the output schema, 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?

Despite an output schema existing, the description supplies the semantics that matter most – gap handling, uncertainty signaling, and a cost unit – leaving no ambiguity about how to interpret or trust results. Complete for a read-only change-audit 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?

Schema description coverage is 100% – entity_id, since, and until all carry their own descriptions and examples. The description restates the same facts (entity_id 'from resolve_company' with the fu_ prefix example, date format, until defaulting to today) without adding syntax or constraint detail beyond the schema, so 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?

States a specific verb and resource with scope ('List what changed at a company since a date') and enumerates the record types covered (status, name, address, legal form, BORME acts). It explicitly names the sibling it is not (lookup_company), so an agent can route without opening either 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 an explicit when ('review a supplier or customer since your last check') and an explicit when-not ('Don't use it for the current state'), plus the alternative to call instead (lookup_company). Nothing 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.