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

The annotations already declare readOnlyHint=true, openWorldHint=true, and destructiveHint=false, so the safety profile is fully covered. The description adds the 'Answers without an API key' fact, which is behavioral context beyond the annotations. However, it doesn't describe what the response looks like (no output schema), nor does it mention rate limits or any other side effects. Since the annotations cover the core behavioral traits and the description adds the API key requirement, a 3 is appropriate.

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 two sentences, with no fluff. It front-loads the core purpose ('Look up a TLS fingerprint') immediately, then provides the key usage constraint ('without an API key') and a concrete example. Every sentence carries meaningful information, and the example call at the end is a helpful, non-redundant addition. This is a model of conciseness.

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 single-parameter, read-only lookup tool, the description is nearly complete. The schema covers the parameter fully, and annotations cover the behavioral contract. The description adds the API key fact and a concrete example, which covers the essential usage context. The only minor gap is that the return format is not described, but since there is no output schema, the agent must infer it. Given the simplicity, this is acceptable, so a 4 is appropriate.

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 schema description coverage is 100%, so the parameter 'input' is fully described in the schema as 'The indicator to look up: a domain, an IP address, an ASN or a file hash.' The description repeats this by showing an example with 'ja3:771,4865-4866-4867,' which confirms the format for TLS fingerprints. This adds some value by illustrating the exact input format for this tool, which the schema does not show. Since the schema covers the parameter semantics and the description reinforces with an example, a baseline 3 is 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 begins with a specific verb and resource, 'Look up a TLS (JA3/JA4) fingerprint,' which is clear. The sibling list includes other lookup tools like whisper_lookuptorrelay, so the inclusion of JA3/JA4 distinguishes it from those. The description also names a specific format for the input, which further differentiates it and adds clarity.

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 states that the tool 'Answers without an API key,' which provides a clear condition for when to use it versus tools that do require a key (though no sibling explicitly mentions API keys, this is useful context). It doesn't explicitly name alternatives or say 'use this instead of X,' but the context and the 'without API key' hint provide clear guidance on when to choose this tool over others that might need authentication. The example call also shows the expected input format, which helps the agent understand how to construct the call.

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