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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=true, so the safety profile is covered without the description. The description contributes the return shape hint ('status, fields, dates'), which is useful, but says nothing about not-found behavior or whether a subscriber outside the given list is returned.

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?

A single short sentence with the lookup key front-loaded and a compact parenthetical enumerating returned attributes; nothing is redundant. It is slightly telegraphic but every clause carries information.

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 2-parameter read tool with no output schema, the description covers the basic operation and sketches the returned attributes. It leaves gaps on list_uid's meaning and on error/empty-result behavior, which matter for a lookup-by-identifier tool.

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 50%: subscriber_uid is documented (including its source tools) but list_uid has no description. The description implies list scoping ('subscriber of a list'), confirming why list_uid is required, but adds no format or semantics beyond that. Baseline 3 fits given partial schema documentation.

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 gives a specific verb + resource ('Get one subscriber of a list') and adds the lookup key ('by subscriber uid'), which is enough to tell it apart from list-style siblings like mailblaze_list_subscribers. It stops short of explicitly naming mailblaze_find_subscriber_by_email as the alternative path, so it isn't a 5.

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 only implied: 'by subscriber uid' suggests you already have a uid, and the schema's parameter note points to list_subscribers/find_subscriber_by_email as uid sources. There is no explicit statement of when to pick this tool versus those siblings, nor any precondition about the list_uid scoping.

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