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

The annotations already declare readOnlyHint=true, so the safety profile is known. The description adds valuable behavioral information: 'Returns found=false if missing or expired.' This discloses the return behavior for missing keys and indicates that values can expire, which is beyond what annotations provide. It doesn't contradict annotations and adds meaningful context.

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?

The description is three sentences, each serving a distinct purpose: the first states what the tool does, the second when to use it, and the third what it returns. It is front-loaded with the core action and contains no filler or repeated information from the schema. Every sentence earns its place.

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?

This is a simple read operation with strong annotations and complete schema coverage. The description covers the key usage context (restoring state at start of run) and the edge case (missing/expired). No output schema exists, but the description's mention of 'found=false' suffices for this simple tool. It is complete for an agent to invoke 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?

Schema description coverage is 100%, with both 'key' and 'namespace' clearly described in the schema. The tool description itself does not elaborate on parameter semantics, but the schema already provides sufficient meaning. According to the rubric, when schema coverage is high, a baseline of 3 is appropriate.

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 'Retrieve a value previously stored with kv_set', which is a specific verb+resource statement that clearly distinguishes kv_get from siblings like kv_set, kv_delete, and kv_list. It also states the intended use case: 'Call this at the start of a run to restore state, preferences, or progress saved by earlier runs.' This makes the tool's purpose unambiguous.

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 description provides clear context for when to use the tool ('at the start of a run to restore state...'), which is explicit and actionable. It references kv_set as the storing counterpart but does not mention alternatives like kv_list for listing keys or when not to use this tool. This falls just short of a 5 because it lacks explicit exclusions or alternative guidance.

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