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

Annotations already declare readOnly/openWorld/non-destructive, so the safety bar is met. The description adds genuinely new context: default ordering ('newest first by default' / new→old), the endpoint (GET /subscribers), and a short inventory of returned fields. Pagination semantics live only in the schema, not here, which caps it below 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?

Two dense sentences plus a trailing endpoint token; purpose and default ordering are front-loaded with no filler. The 'GET /subscribers' fragment is slightly redundant but harmless. Efficient overall.

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 steps in by enumerating returned fields (e-mail, type, tags, notes, metadata, source, open/click rates, dates) and the default sort. Pagination is covered by the page parameter in schema, so nothing critical is missing; a note on result-size/cursor behaviour would be the only gap.

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 description coverage is 100%, so all nine parameters (tag, page, type, not_type, domain, ordering, created_after/before, email_address) are already fully documented. The description's filter list ('e-mail text, type, tag, signup date or domain') largely mirrors the schema and omits not_type and page, so it adds little beyond the structured fields. Baseline 3.

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 pair ('list or search') and resource ('subscribers'), and the surrounding sibling names (get_subscriber, add_subscriber, update_subscriber) make the singular/single-item and mutation variants trivially distinguishable. An agent can tell this is the collection read endpoint 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?

The filtering sentence implies the tool's role (enumerate/filter subscribers), but there is no explicit when-to-use vs when-not, and no alternative sibling is named for cases like finding one subscriber (get_subscriber) or mutating (update_subscriber). Usage is inferable but not guided.

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