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

Annotations already declare readOnlyHint and openWorldHint, so the safety profile is covered; the description adds genuinely new behavioral context by disclosing the x402 pay-per-call model, the $0.05 USDC price, settlement chains (Base or Solana), and that charges apply only to successful calls. It stops short of saying what a non-existent username returns or whether handles need an '@' prefix.

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 with zero waste: capability first, then the payment condition. Nothing is repeated and the most decision-relevant fact (cost) is placed up front for the caller.

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 one parameter, annotations present and no output schema, the description covers what is returned and the payment mechanics adequately. The remaining gap is edge-case behavior — not-found responses and identifier format — which an agent would want before calling.

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?

There is a single parameter with 100% schema description coverage, so the schema already fully documents 'handle'. The description adds no format detail beyond the schema (e.g. whether '@' is accepted, casing rules), 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 ('Check whether ... exists') and resource ('Snapchat username') and enumerates what is read back (public profile, Bitmoji, Snapcode). It does not name a sibling tool or explain how it differs from osint-username or username_scanner, so an agent must infer the distinction from the platform name alone.

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 only implied: the description makes clear this is a platform-specific existence/profile lookup, and the pricing sentence hints at the no-API-key path. There is no explicit 'use this instead of X when...' guidance nor any stated preconditions or exclusions relative to the many other username-scanner siblings.

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