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

With no annotations provided, the description carries the full burden. It discloses that this is a write operation, that it merges without affecting other fields, that it is free, and that proof of npub ownership is required. It also flags the sensitive nature of the credential vault. It does not detail failure modes or whether the operation is idempotent, but the merge semantics and proof requirement are meaningful behavioral disclosures beyond the schema.

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 compact and front-loaded: the core action is in the first sentence, followed by merge semantics, use cases, cost, and auth requirement. Every sentence earns its place, and the warning about the sensitive vault is placed at the end as a natural emphasis. No fluff or repetition of schema details.

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?

Given the tool's complexity (4 required params, sensitive write, no annotations), the description covers the key operational context: what it does, merge behavior, use cases, cost, and proof requirement. The output schema exists, so return values don't need explanation. A minor gap is that it doesn't mention what happens if the field already exists (overwrite vs. merge) beyond 'merges', and it doesn't state whether the operation is reversible, but these are not critical for an agent to invoke it correctly.

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 description coverage is 100%, so the baseline is 3. The description adds value by explaining the merge behavior and the purpose of the field/value pair, and it reinforces the dpop_token requirement contextually. However, it doesn't add much detail about the 'field' parameter's allowed values or format beyond the schema, and the dpop_token schema description is already very detailed. The description's contribution is moderate but real.

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 ('Add or update'), a specific resource ('a single patron credential field'), and the merge semantics ('Merges into existing stored credentials without affecting other fields'). It also gives concrete use cases (setting an account identifier after OAuth, changing a default brain), which distinguishes it from sibling tools like goodearth_delete_patron_credential or goodearth_get_patron_credential_fields.

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 clear context for when to use the tool ('after OAuth', 'changing a default brain') and states it is a write to a sensitive vault. It does not explicitly name sibling alternatives or state when NOT to use it, but the use cases and merge semantics imply the distinction from delete/get credential tools. A small gap: it doesn't mention that this is for a single field vs. bulk operations, though 'single patron credential field' covers that.

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