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

Annotations already declare readOnly/idempotent/non-destructive/closed-world, and the description adds the resolver-hit vs. resolver-miss semantics that annotations cannot express: a lookup against ptpge.org/f/, self-registration within seconds, and status 'unknown' for an unregistered-but-valid fingerprint. That is precisely the extra context the annotations cannot carry.

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 tightly packed sentences, front-loaded with what the tool does and what it returns, then the lookup-vs-inversion caveat and the unknown-status case. Dense with parentheticals but no sentence is filler; a slight readability cost from jargon like 'MIS/ERP' keeps it off a 5.

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 no output schema, the description carries the return contract well — it lists the expansion fields and the 'unknown' status path. The only real omission is any guidance on the `language` parameter and the exact shape of a hit vs. miss response.

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?

Schema coverage is 50%: `fingerprint` is documented in the schema and the description restates its accepted forms (ptpge-cfs/1, 64-hex, 16-hex short form, optional resolver URL prefix), which is useful but largely overlapping. The `language` parameter is undocumented in both the schema and the description, so the gap is not compensated.

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 and resource ('expand a fingerprint ... back into its structured configuration') and enumerates the returned structure (matched profile, product, bindings, canonical string, dataset version). It also explicitly distinguishes itself from the inverse operation and from ptpge_fingerprint, so an agent can pick it out of the sibling list without opening a schema.

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?

Names the use case ('read-back path for MIS/ERP'), names the alternative that it is not ('not an inversion of the hash'), and ties itself to the sibling that feeds it ('every fingerprint computed by ptpge_fingerprint is self-registered within seconds'). An agent knows both when to call it and what a miss means.

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