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

Annotations already declare readOnlyHint=true, and 'Read-only' in the description merely restates that. The one genuinely additive piece is the underlying API mapping (GET /campaigns/{campaign_id}), which gives the agent endpoint-level context, but nothing is said about not-found/error behavior beyond that.

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 clauses with zero filler, and the core purpose is front-loaded in the first sentence ahead of the read-only note and endpoint reference.

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 single-parameter read tool with annotations covering the safety profile and no output schema to explain, this is essentially complete: it states what it returns (a campaign), how to identify it (id), and the backing API endpoint. Only minor gaps, such as error behavior, remain.

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% with a single parameter ('Campaign id.'), so the schema fully documents the input. The description's 'by id' adds no format, source, or constraint detail beyond it, so 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 and resource ('Fetch a single campaign by id'), and the 'single ... by id' phrasing implicitly separates it from the sibling mailerlite_list_campaigns. It stops short of naming the alternative explicitly, but an agent can tell a by-id fetch from a list without opening either 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?

Usage is implied by the fact that the tool takes a single campaign_id, so it is clearly the by-id lookup as opposed to a listing. However, there is no explicit statement of when to use this vs mailerlite_list_campaigns, and no mention of prerequisites such as the campaign having to exist.

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