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

Annotations already signal readOnly, idempotent, non-destructive behavior carrying the safety profile. The description adds meaningful behavioral detail beyond that: 'Returns one row per DOCUMENT', the PL number/territory/date/PDF link fields, and the fact a product usually has multiple document types. It does not fully describe paging or ordering, but those are minor.

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?

Every sentence earns its place: scope, post-Brexit rationale, output row semantics, and sibling routing. The key verb and resource are front-loaded, and there is no filler or redundant repetition of the schema.

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 read-only search tool with no output schema, the description explains what is searched, how results are shaped (one row per document), what fields each row includes, and how to use the related mhra_product tool. Combined with fully documented parameters and aligned annotations, an agent has enough to invoke it correctly.

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 covers all five parameters at 100%, so the baseline is 3. The description adds value beyond the schema by clarifying what can go in the query ('product name, brand name or active substance') and by explaining the document-type concepts (SmPC, patient leaflet, assessment report) that map to the doc_type parameter.

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 opens with a specific verb and resource: 'Search the UK MHRA products register by product name, brand name or active substance', and includes concrete examples. It also distinguishes itself from sibling tools by ending with 'Use mhra_product to gather every document for one PL number.'

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 provides explicit when-to-use context ('Post-Brexit the EMA register does not cover the UK, so this is the UK authorisation surface') and names the sibling alternative for a different need ('Use mhra_product to gather every document for one PL number.'). This gives an agent clear decision guidance.

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