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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint=false, so the safety profile is covered by structured data. The description adds only the dependency on search-issued ids and the 'compatibility tool' framing; it offers no further behavioral detail such as error behavior for unknown ids or what 'full details' comprises.

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?

A single tight sentence with no filler; the pairing constraint and the retrieval action are both stated in one pass, and nothing is redundant.

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?

With one fully documented parameter, a complete annotation set, and an output schema that handles return values, the description covers what an agent needs to invoke it correctly. Only marginal enrichment (error cases, id provenance edge cases) is absent, which is acceptable at this complexity.

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?

There is a single parameter fully documented in the schema (100% coverage), including the '<postcode>|<product_id>' format, so the schema carries the semantics. The description echoes the id's provenance from search but adds no format or validation detail beyond it, making 3 the correct baseline.

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 (retrieves), a precise resource (the full details of one broadband deal), and the scoping mechanism (by its id, from results returned by search). This distinguishes it cleanly from sibling `search`, which returns the list, without the agent needing to open 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?

It states the tool is paired with `search` and operates on a deal id that search returned, which clearly signals the intended call sequence (search first, then fetch). It stops short of an explicit when-not-to-use statement or naming `check_fibre_availability` as an alternative, so it falls short of a 5.

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