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

Adds real context beyond annotations by disclosing partial-update semantics ("only the values to change") and the scope boundary around subscription status. However, annotations declare destructiveHint=true and the description never explains what that means here – e.g. that sending first_name/last_name overwrites existing values and blanking is not possible – so an agent could read this as a harmless patch.

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 sentences with the operation type and mutable fields front-loaded, then the parameter rule, then the exclusion. No filler, and every clause carries distinct 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?

Covers the hello-world of the call – what can change and what cannot – for a tool with a nested custom_fields object and no output schema. It omits behavior when the subscriber or list_uid does not exist, what the response contains, and any mention of the destructive overwrite semantics, which is meaningful for a 6-parameter mutation.

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 only 33%, and list_uid and subscriber_uid have no description in either the schema or the description, leaving two of three required parameters unexplained. The description does add the useful "only the values to change" semantics and reinforces the required-email rule (which the schema also states), partially offsetting the coverage gap.

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?

Opens with an explicit "WRITE:" marker followed by a specific verb and resource ("update a subscriber's name or custom fields"), so the mutation type and editable surface are unambiguous. The closing clause "Does not change subscription status" separates it from mailblaze_unsubscribe_subscriber and mailblaze_resubscribe_subscriber without those tools being named.

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?

Gives a clear selection context: send only the fields to change, plus the email Mail Blaze requires. "Does not change subscription status" implicitly routes status changes elsewhere, but no sibling tool is named explicitly and no prerequisite (e.g. subscriber must already exist in the list) is stated.

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