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

Goes well beyond the readOnly/openWorld annotations: discloses data richness (reaction/comment/share counts, conditionally rendered), a rendering cap on logged-out visitors, empty results for private groups, the no-login policy, and the 1-credit cost. This is exactly the behavioral context an agent needs.

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?

Front-loads the resource definition, then layers in limits and cost. Four sentences with little waste, though the page-posts comparison is slightly tangential.

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?

For a tool with no output schema, it adequately describes returned data, rendering limits, failure modes (private groups), and cost. The only missing piece is meaning for the undocumented cache_max_age parameter.

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 url parameter already has a schema description ('Group URL, group id, or group slug'), and the prose adds nothing more. The cache_max_age parameter has no schema description and is not explained in the description, so at 50% coverage this leaves a real gap unaddressed.

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+resource: recent posts from a public Facebook group. It distinguishes scope (public only) and references the analogous /v1/facebook/page-posts limit. It doesn't explicitly contrast with facebook_group or other siblings, but the resource is unambiguous.

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 conveys key constraints (public only, private groups return empty) that effectively say when this will or won't work. However, it doesn't name alternatives such as facebook_group for group details or what to do for private content, leaving routing to inference.

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