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

Annotations already declare readOnlyHint and openWorldHint, but the description adds genuinely non-derivable behavior: the data source is the public web profile page, the cost is $0.002 USDC per successful call via x402 on Base/Solana/Arc, and failed calls are free. It does not mention rate limits or auth prerequisites beyond the payment rail, which keeps it just under 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?

Two sentences, front-loaded with the return contents, followed by exclusions and then cost – each clause carries information an agent needs. No filler or repetition of the title.

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?

An output schema exists, yet the description still summarizes the returned fields, and it covers the two things structured fields cannot: what is absent from the public page and the per-call cost. Nothing essential for correct invocation is missing.

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 single `username` parameter has 100% schema description coverage including format constraints (3-15 letters, digits, . _ -, no @). The description adds no further syntax or edge-case guidance beyond the schema, so the baseline 3 applies.

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 and resource ('Public Snapchat profile from its web profile page') and then enumerates exactly which fields are returned (username, display name, page title/description, snapcode, canonical link). No sibling tool shares that subject matter, and the field list lets an agent confirm the resource is the one it wants without opening the 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?

Gives a clear positive condition (public profile data only) and an explicit negative scope: Stories, Spotlight posts and follower counts are not shown and not returned, which steers the agent toward other tools for those needs. It stops short of naming an alternative (e.g., social_socialblade) for follower metrics, so no explicit routing is provided.

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