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

Annotations already declare readOnlyHint=true and openWorldHint=false, so safety is covered. The description adds substance beyond that by enumerating what the response contains (limits, media kinds, required fields, placements), which matters because there is no output schema. It omits nothing critical for a no-param read.

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 sentences, no filler. The resource and its returned rule categories come first, and the usage nudge is placed last as a takeaway.

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 carries the burden of saying what comes back, and it does so by listing the rule categories. Combined with annotations covering the read-only, non-open-world profile, an agent has everything needed to call it correctly.

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, so there is nothing to disambiguate; the baseline for 0-param tools is 4. The description correctly implies no filtering or selection is needed.

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 resource (every network Mellow publishes to) plus the payload of rules it returns (caption limits, media counts/kinds, required fields, placements). That is concrete enough to separate it from siblings like validate_post or create_post without opening a 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?

"Read this instead of guessing a limit" gives a clear condition for invocation: consult it before asserting any platform constraint. It does not name a sibling alternative or state exclusions (e.g. whether validate_post already enforces these), so it stops short of explicit when/when-not routing.

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