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

Annotations already declare readOnly/idempotent/non-destructive/openWorld, but the description adds non-obvious behavioral facts: it is documented as NOT gated by the Send Message module, and only write operations in this category surface a module-not-enabled 403. That 403-routing caveat is valuable context beyond the annotations. It stops short of a full return-shape description, so not 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?

Three short paragraphs, front-loaded with what is returned and then the routing/error guidance. Every sentence carries information, though the 403 caveat is somewhat dense and could be slightly tighter.

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 present, the description compensates by enumerating the returned state fields and explaining how to interpret a 403 response. For a zero-parameter, read-only diagnostic tool this covers everything an agent needs to call and act on it.

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?

The tool takes zero parameters, which is the baseline-4 case. The description reinforces this with 'Takes no parameters', leaving nothing ambiguous about invocation arguments.

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 (read) and resource (account messaging state) and enumerates the exact facets returned: module access, allowed channels, monthly email/SMS allowance, 10DLC sender readiness, and active pause. This is clearly distinguishable from siblings like get_plan, get_business, and health_check.

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 explicit invocation timing ('CALL THIS FIRST whenever a send is refused or before promising a send will work') and positions itself against guessing or other tools by claiming to be the only tool that identifies which cause produced a 403. It also warns that a 403 here does not imply the module is off, which is real when-not guidance.

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