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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint, so the safety profile is known. The description adds meaningful behavioral context: it says 'without charging' and clarifies that 'A returned offer is not purchase authorization.' This goes beyond the annotations by specifying that no charge occurs and that the return is not a binding purchase, which is valuable for an agent deciding to call this tool.

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 concise and front-loaded with the core purpose. The first sentence states the function clearly. The second sentence provides usage context and a critical caveat. The empty 'Example: {}' is a minor structural flaw, but overall the description is efficient with no wasted words.

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?

Given there are no parameters, no output schema, and annotations cover safety, the description covers the essential points: what it returns, when to use it, and a key caveat about authorization. It doesn't specify the exact return format, but for an informational tool like this, the description is sufficiently complete for an agent to invoke it correctly.

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 tool has zero parameters, so the schema is fully covered (100%). The baseline for 0 parameters is 4, and the description doesn't need to explain parameters. It adds no parameter-specific meaning, but there's nothing to add, so the baseline 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?

The description clearly states the tool returns free and paid boundaries and purchase routes, with the specific verb 'Return'. It distinguishes itself from siblings by focusing on offering information about plans and routes, not checking or creating. The phrase 'without charging' adds clarity. However, it could be more explicit about what 'boundaries' means, and the empty example is a minor flaw.

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?

The description gives explicit context on when to use the tool: 'Read this for the free daily plan, $9 paid pass, human checkout and agent payment route.' This tells the agent exactly what scenarios this tool serves. It doesn't mention alternatives or exclusions, but the context is clear enough for an agent to select it over siblings like fluxproof_check_now or fluxproof_preflight.

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