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

With no annotations, the description carries the full burden and does well: it discloses that the substrate performs the fetch, that it's public with no bearer required, that it shares the crypto pipeline, and warns of a false-negative failure mode from body paraphrasing. It also names the extra return fields (`credential_url`, `credential_bytes`), though it doesn't discuss rate limits or fetch failure behavior.

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 'When to use' framing is front-loaded and the rationale is concrete. It is somewhat dense with parentheticals and repeated restatements of the fetch behavior, so a little trimming is possible, but every sentence contributes.

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?

No output schema exists, and the description compensates by stating the return envelope and the two extra fields. Combined with the auth note and failure-mode warning, an agent has enough to call it correctly, though return-value details remain summarized rather than structured.

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 100%, so both parameters are already documented in the schema, including the optionality and JWKS-derivation behavior of `jwks_url`. The description reinforces the semantics ('pass only the URL, never the JSON body') but adds little syntax or format detail beyond the schema, so the 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 states a specific verb+resource ('Verify a credential by URL') and immediately clarifies the key differentiator: the substrate fetches the body itself rather than accepting JSON. It explicitly distinguishes itself from the sibling `verify_credential` by naming it and contrasting the fetch model.

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 has an explicit 'When to use' clause, names the alternative (`verify_credential` with the same crypto pipeline), and gives concrete conditions that select this tool (credential too large, or client may paraphrase/trim the body causing false `valid: false`). Nothing is left to inference.

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