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

readOnlyHint=true already covers the safety profile, but the description adds real value by disclosing the payload contents (state, value, parties, close date) and the backing endpoint POST /v1/rex/Deals/read. This matters because there is no output schema, so field disclosure comes only from the description. It does not mention not-found/error behavior.

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?

Three compact clauses with no filler; the resource and its scope lead, the return fields follow, and the provenance hint closes. 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?

For a one-parameter read tool with no output schema, the description covers what it returns, where the key comes from, and the underlying endpoint. Only failure modes and access restrictions are unaddressed, which is a minor gap.

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 coverage is 100% and the id parameter is documented there, so the baseline is 3. The description goes one step further by explaining where the id originates (a prior search or autocomplete), which the schema does not convey.

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 ("One deal by id") and enumerates the returned fields (state, value, parties, expected close date). It implicitly distinguishes itself from the many rex_search_* siblings by being a single-record fetch keyed on id, though it never names rex_search_deals explicitly.

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 id comes from a search or autocomplete" makes the prerequisite workflow explicit, telling the agent it must first run a lookup rather than guess an id. It stops short of naming rex_search_deals as the alternative or stating any when-not conditions.

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