Bulk update subscriber custom field values

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

Annotations already flag destructiveHint=true and idempotentHint=false, but the description adds concrete consequences (delivery, audience membership, published data, irreversible state) plus a hard auth constraint (OAuth only, no API keys). This goes meaningfully beyond the structured hints.

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?

Four tight sentences, purpose first and warnings after, no filler. Every sentence carries information, though the warning list reads slightly like a template.

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 and a nested bulk payload, the description covers impact and auth but says nothing about the asynchronous nature implied by callback_url, result/status reporting, or batch limits. Adequate but with clear gaps for a 6-parameter nested 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 description coverage is 67%, near the baseline where the schema does most of the work. The description reinforces the confirm=true requirement, but adds no meaning about payload vs payload_file vs body-flag alternatives or the callback_url field beyond what the schema already states.

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 states a specific verb (bulk update), resource (subscriber custom field values), and scope (bulk), which clearly separates it from siblings like bulk_create_custom_fields, update_custom_field, and update_subscriber. It is clear but does not explicitly name or contrast with those siblings.

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?

It supplies invocation prerequisites (confirm=true, OAuth required, API keys unsupported) but gives no guidance on when to prefer this bulk endpoint over single-subscriber alternatives or when it should be avoided. Usage context is implied by the bulk framing only.

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