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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), but the description adds substantial behavior the annotations cannot convey: it is a polling loop, which states are final, backoff cadence, and a hard time limit with a do-not-resend rule. That is exactly the extra context an agent needs to avoid hammering the endpoint or double-sending.

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 purpose, then the polling protocol in three tightly packed sentences. No filler; the timing numbers and terminal-state list are the operative content and every clause is actionable.

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?

No output schema exists, so the description carries the return-value burden — and it does so by enumerating the status lifecycle the caller will observe. Combined with the timeout and backoff guidance, an agent has everything needed to invoke and interpret this tool 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 coverage is 100%, so the baseline is 3; the description goes beyond it by adding a cross-parameter constraint the schema does not state — the key must belong to the same project as the message being read. That reframes api_key as scoping rather than mere auth, which is a genuine, if modest, addition.

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 ('current state of a message'), and anchors the resource to 'a message sent with a key of the same project', which ties it directly to the send_message sibling. An agent can immediately tell this is the read/poll counterpart to send_message, not a send or key-creation tool.

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?

Exceptionally explicit: it says to poll only while status is queued or submitted, names the terminal states (delivered, undeliverable, failed) and the never-changing state (unknown), prescribes backoff (start ~2s, double, cap at 30s), and gives a timeout policy with the correct fallback action (treat as unconfirmed, do not resend). This is a complete when/when-not/how-often protocol.

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