Add segment members

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

Annotations already declare readOnlyHint=false, idempotentHint=true, destructiveHint=false, so the safety/mutation profile is covered. The description adds genuinely useful behavior beyond that: the 500-email-per-call limit and the createMissing flag governing whether unknown addresses become new contacts. The 'Returns' line is vague, which keeps this from a 5.

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 a labeled Purpose/Not-for/Use-when structure that scans quickly and wastes little space. The 'Returns' sentence ('The result of the membership change') is empty filler that slightly dilutes it.

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, but the description scopes the operation, limits, and the createMissing behavior well. The one gap is the undescribed `subscribed` flag, which could affect whether added contacts receive email, so it is not fully complete.

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 75% and the description reinforces key semantics (max 500 emails, createMissing meaning). It adds context beyond the schema for createMissing and the email cap, but says nothing about the undocumented `subscribed` parameter, so it doesn't fully compensate.

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 ('Add contacts to a STATIC segment by email address') and immediately distinguishes the scope from plunk_update_segment for dynamic segments. An agent can tell what this does and how it differs from siblings without opening a 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 provides when to use ('hand-curating an audience, or importing a list') and when NOT to use ('Not for: a DYNAMIC segment... use plunk_update_segment instead'). Names the concrete alternative tool, leaving nothing to inference.

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