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

Annotations already indicate destructiveHint=true and idempotentHint=true. The description adds behavior on omitted fields, blank values, and rejection of invalid values, which is helpful. No contradiction with annotations.

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?

The description is well-structured with the main action first. However, it contains seven sentences, some of which are redundant (e.g., effect and retry advice). Could be more concise.

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?

While annotations and output schema exist, the description covers permissions, effects, and idempotency. However, the inaccurate claim about tags/sequences creates a completeness gap. It adequately describes behavior but lacks clarity on those unsupported parameters.

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% but the description claims the tool updates tags and sequence assignments, which are not present in the input schema. This is misleading. The description does add meaning for custom field behavior, but the inaccuracy reduces usefulness.

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 clearly states the tool updates profile fields, status, custom fields, tags, or sequence assignments for a single subscriber. This distinguishes it from sibling tools that focus on one specific action (e.g., subscribers_add_tag, subscribers_update_status).

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 description explains that omitted fields remain unchanged and blank optional custom field values are kept, which guides usage. It also mentions retrying after reading current resource state. However, it does not explicitly contrast with dedicated tag/sequence tools, leaving some ambiguity.

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