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

Annotations already cover readOnlyHint=true, but the description adds genuinely new context: the returned content is untrusted (a prompt-injection warning) and the call has no side effects on registration or expiry. It does not describe behavior on an expired or missing key, which is the remaining gap.

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 short sentences, zero filler, with the core action front-loaded and the constraints trailing. Every clause adds information an agent needs.

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 scope, security posture, and non-behaviors adequately. The only shortfall is the absence of any hint about failure modes for expired/invalid keys.

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 0%, so the bare 'key' string carries no documentation. The description partially compensates by mapping it to the X-Context-Key header, which tells the agent where the value comes from, but it omits format, validation, or expiry-related semantics for the key.

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 (Read) and resource (guest text entry), plus a scope qualifier (unexpired) and the mechanism (X-Context-Key). It also distinguishes itself from nearby siblings by declaring what it does not do: it does not register an agent or renew expiry, unlike register_agent or a renewing operation.

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 establishes the applicable condition (the entry must be unexpired) and two explicit exclusions (no agent registration, no expiry renewal), which steers the agent away from misusing it. It stops short of naming the sibling to use instead (e.g., save_guest_context for writing), so it is clear context without full alternative routing.

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