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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=false, so safety is covered structurally. The description adds non-obvious behavioral context the annotations cannot convey — a Pro plan or higher entitlement requirement — which is exactly the kind of gating an agent needs before invoking.

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 with no waste: the primary purpose and id formats come first, then the entitlement constraint. Nothing is repeated from the schema or annotations.

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 single-parameter read whose output schema is provided and whose safety profile is in annotations, the description covers what's needed: provenance of the id, accepted formats, and the plan gate. Minor gaps remain around error behavior for invalid or cross-account ids, but nothing essential is missing.

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%, so baseline is 3, but the description goes beyond the schema's generic 'composite id returned by the search tool' by spelling out the four accepted prefixes. That prefix enumeration is genuine added meaning for constructing a valid id.

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 (fetch) and resource (the full record behind a search result id), and enumerates the id namespaces it accepts (campaign:, affiliate:, coupon:, conversion:). This distinguishes it clearly from sibling getters like get_campaign or list_coupons, which target a known entity type rather than a search-result composite id.

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?

Explicitly ties the tool to a preceding search result id, which tells the agent when to use it (after search) and what input it expects. It doesn't name an alternative for cases where the agent already knows the entity type, but the linkage to search is a clear usage condition.

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