What this costs before you spend anything

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

The description states the tool is free, which is a key behavioral trait. However, with no annotations, it doesn't disclose auth requirements, side effects, or whether results are cached or dynamic. This partial transparency is adequate for a simple cost-checking 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 a single sentence front-loaded with 'Free.' It wastes no words while conveying purpose, output, and usage context. Every word earns its place.

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 zero parameters and no output schema, the description sufficiently covers what the tool returns and when to use it. It lacks details about response format or authentication, but the low complexity makes it complete enough for a simple info tool.

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?

With zero parameters, the input schema requires no explanation. The description adds value by specifying what the tool returns, which is not parameter semantics but does inform the agent's decision to call it.

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 specific information (prices, size limit, chain, payment) and positions it as a free decision support tool before using paid tools. This distinguishes it from siblings transcribe_url and find_dead_air, which have different purposes.

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 explicitly tells the agent to use this tool before calling paid tools to decide if they are needed. While it doesn't list exclusions or alternative tools, the context of preventing unnecessary paid calls is clear and actionable.

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