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

Annotations already cover safety (readOnlyHint) and open-world scope, so the description's job is to add traits: it discloses the hard 3-row cap, the daily refresh cadence, the UK geographic scope, and that the paid feed is the full-data counterpart. It does not describe the returned record shape, which matters since there is no output schema.

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 short sentences, no filler, and the key constraint (free, max 3 rows) is front-loaded before the filter-parity note. Every clause carries information.

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 simple 4-optional-parameter read tool with no output schema, the description covers source, scope, row cap, and filter behavior. The remaining gap is the shape of the returned rows, which neither the description nor an output schema supplies.

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 50% — types and postcode are documented in-schema, while industry (enum only) and locality carry no text. The description adds only the pointer that filters match companies_changes_feed, which hints at filter parity but gives no semantics for the two undocumented parameters.

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 — returns up to 3 rows from the daily UK director and owner changes feed — plus the free-tier cap and the exact sibling whose filters it mirrors. An agent can distinguish it from companies_changes_feed and companies_changes 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?

"Try before you pay" plus "same filters as companies_changes_feed" makes the evaluation use case and the paid alternative clear. It stops short of an explicit instruction such as "switch to companies_changes_feed when you need complete results," leaving that inference to the agent.

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