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

Annotations already declare readOnly, idempotent, non-destructive, closed-world behavior. The description adds genuine context beyond that: the exact key name is required, and the response preserves the original Content-Encoding with most clients decompressing automatically. That encoding note is real operational value an agent would otherwise not know.

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?

Front-loaded with the core action and scope, then a short behavioral note, then usage. The USAGE line slightly overlaps the first sentence, but the examples earn their space by showing realistic inputs. No filler.

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 an output schema present there is no need to describe return values, and the annotations carry the safety profile. For a two-parameter read tool, the description supplies everything else an agent needs: exactness of the key, allowed value types, and the encoding caveat.

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 100%, so the baseline is 3. The description still adds a semantic constraint the schema omits — that the key must be an exact match — and the examples show the 'username~my-store' form of the store ID, gently reinforcing the ID format.

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?

Specific verb (get) + resource (value under a key in a key-value store) with an explicit scope boundary: 'a single record, not a listing of all keys.' None of the sibling tools overlap with this resource, and the anti-scope clause removes any ambiguity about whether it enumerates keys.

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 USAGE line gives a clear triggering condition — retrieving a specific record (JSON, text, or binary) — and two concrete examples anchor it. It lacks explicit when-not-to-use guidance or named alternatives, but no similar sibling exists to route against.

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