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

With no annotations provided, the description carries the transparency burden. It discloses that the tool returns previously gathered observations rather than performing a new action, and it clarifies that all returned data is public CC0. It does not explicitly mention lack of side effects, rate limits, or error behavior, but the 'already observed' framing and no-token/no-arguments guidance strongly imply a read-only, low-risk call.

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 front-loaded with the main purpose and packs many useful details into a compact paragraph. The costume metaphor and parenthetical add a little flair, but they meaningfully explain the difference between User-Agent claims and TLS/JA4 properties rather than padding the text.

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?

Since there is no output schema, the description acts as the output preview and lists all major return categories: User-Agents, JA4 fingerprint, network, cataloging, and shared fingerprint identity. It also covers data licensing. It does not explain empty-result behavior or error conditions, but for a zero-parameter self-lookup tool the description is sufficiently complete.

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 already has zero properties and 100% schema_description_coverage, so the agent knows there are no parameters; baseline is 4. The description reinforces this with 'no token, no arguments, one call', clarifying that not even an auth argument is expected. It adds no new parameter-specific semantics, but that is not needed for an empty parameter schema.

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 states a clear action, 'Ask what The Fomite has already observed about YOU, the caller', and enumerates the concrete outputs: User-Agents, JA4 fingerprint, network, cataloging, and shared fingerprint identities. It clearly distinguishes itself as an introspection endpoint with 'no token, no arguments, one call', though it does not explicitly compare itself to similar sibling names like fomite_whatami.

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?

It gives clear context for when to use the tool: when you want the stored observations about the calling identity. The call constraints ('no token, no arguments, one call') are practical guidance. However, it does not explicitly state when not to use it or name alternatives, so it lacks a full when-to-use/when-not-to-use decision rule.

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