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 this is a write to a sensitive credential vault, requires proof of npub ownership, is free, and merges without affecting other fields. It does not explicitly state whether an existing field is overwritten or whether the change is reversible, which keeps it from a 5.

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?

Five short sentences, each earning its place: purpose, merge behavior, use cases, cost, and security requirement. The most important identifying information is front-loaded in the first sentence.

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 sensitive write tool with no annotations, the description covers what, why, merge semantics, cost, and auth. It is missing explicit routing to alternatives like delete_patron_credential or get_patron_credential_fields for adjacent needs, but an output schema exists and parameter coverage is complete, so the gap is minor.

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 the schema already documents npub, dpop_token, field, and value. The description mentions credential fields and merge behavior but adds no parameter-level meaning beyond what the schema properties provide, matching the baseline for full schema coverage.

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 opening line, 'Add or update a single patron credential field,' states a specific verb and resource, and the 'single patron credential' scope distinguishes it from sibling credential tools like delete_patron_credential, get_patron_credential_fields, and update_operator_credential without needing to inspect their schemas.

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 gives concrete use cases ('setting an account identifier after OAuth, changing a default brain') and clarifies merge semantics, so an agent knows when it applies. It does not explicitly name alternatives or state when not to use this tool, stopping short of a 5.

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