Read performance of a post on X

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

Beyond the readOnlyHint/openWorldHint annotations, the description discloses key behavioral traits: that private metrics are served with the user-context connection, that missing data must never be reported as zero engagement, that it costs credits, and that X must be connected. This is valuable context the annotations do not convey.

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?

The description is dense but every sentence carries actionable information. It front-loads the core purpose and metric list, then priorities, then caveats. Slightly lengthy, but no fluff or repetition—appropriate for the complexity.

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?

Without an output schema, the description covers what metrics are returned, when data is missing and how to interpret it, credential prerequisites, cost implications, and how to switch to the correct sibling tool. All critical operational details are present.

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 schema already provides detailed descriptions for both parameters (id as numeric post id from URL, publishedAt as epoch ms for 30-day window). The description reinforces the purpose of publishedAt ('inside X's 30-day window instead of costing a refused call') and connects it to the tool's behavior, adding clarity beyond the schema.

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 opens with a clear statement of what the tool does: 'Read performance of a post on X' and enumerates the exact metrics (impressions, likes, reposts, etc.). It also distinguishes itself from the retired sibling x_post_insights, making its role 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?

Explicitly instructs 'Prefer this over x_post_insights' and notes that x_post_insights' endpoint family is retired. It also specifies when the private advertiser metrics are available (own posts in last 30 days) and cautions about missing data for deleted/protected/suspended posts.

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