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

readOnlyHint=true already tells the agent this is a safe, non-mutating read, so the description's main added value is the explicit GET endpoint and the enumeration of returned fields. It does not disclose error behavior (e.g. 404 for a bad id) or any auth/rate-limit characteristics, so with annotations carrying the safety profile this sits at a solid but unremarkable 3.

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 tight sentences with zero filler; the payload summary is front-loaded and the sibling routing plus endpoint form a useful trailing clause. 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?

With no output schema, the description compensates by enumerating the returned fields, and with one fully-documented parameter there is little else an agent needs. Minor gaps remain around failure modes and pagination-free single-object retrieval, but nothing essential to calling it correctly 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% and the single campaign_id parameter is fully documented in the schema, including its UUID pattern and its origin in smsmode_list_campaigns. The description adds no format or sourcing detail beyond that, so the schema does the heavy lifting and the baseline 3 applies.

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+resource ('Get an SMS campaign') and enumerates exactly what the caller receives: state, period, recipients count, text, price and per-status delivery counts. This clearly separates it from smsmode_list_campaigns (many campaigns) and smsmode_list_messages (individual messages), so an agent can pick it without opening the schema.

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 routes the agent to smsmode_list_messages with campaign_id when individual messages are wanted, which is the key branch point. It stops short of a full when/when-not statement (e.g. no guidance on what happens for an unknown or scheduled campaign id), but the context is clear.

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