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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, covering the safety profile. The description adds useful behavioral context by clarifying that it operates 'without reading anything' and reports cost in credits, though it does not specify whether calling the estimate itself consumes credits or how exact the estimate is.

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 a single, front-loaded sentence with zero wasted words. It immediately communicates the tool's purpose and key behavioral distinction.

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 simple two-parameter estimation tool with full schema coverage and clear annotations, the description is nearly complete. It states the tool returns a credit cost without performing a read, though with no output schema it could more explicitly describe the response format or estimation fidelity.

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 100%, so both parameters ('platform' and 'limit') are already documented in the input schema. The description does not add any further meaning, formatting, defaults, or constraints beyond what the schema provides, making the baseline 3 appropriate.

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 action ('says what ... would cost in credits') and resource ('reading someone’s posts'), clearly indicating a cost-estimation tool rather than a scraping tool. It implicitly distinguishes itself from actual scraping via 'without reading anything,' but does not explicitly name a sibling like scrape_posts or the other estimate_* tools.

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?

Usage is implied: use this to preview credit cost before reading/scraping posts, since it explicitly says 'without reading anything.' However, there is no explicit guidance on when to choose this over scrape_posts or the sibling estimate_image_cost, estimate_source_cost, or estimate_video_cost tools.

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