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

Annotations already declare readOnlyHint=false, idempotentHint=true and destructiveHint=false, so the overwrite semantics are partly covered. The description adds genuinely new context: 'Nothing is sent to Cairn' (no network egress) and the safety constraint that the wallet must be a PUBLIC address, not a key. Return format and storage details are not described, keeping this short of 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?

Front-loaded with the action, followed by the sibling disambiguation, the privacy guarantee, and the wallet caveat in four tight sentences. The final wallet fragment slightly duplicates the schema but is defensible as a safety reminder.

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 7-parameter nested-object write with full schema coverage and no output schema, the description covers purpose, alternative routing, privacy, and the wallet safety caveat. What remains unstated (confirmation of storage location, error behavior) is minor given the annotation and schema richness.

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%, with all seven parameters documented including the nested wallet object, so the schema carries the load and baseline 3 applies. The description's wallet note ('PUBLIC address only') largely repeats the schema's own address property description rather than adding new syntax or constraints.

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 ('Build this agent's Agent Card and save it in the user's private storage') plus the key scope detail that it replaces an existing card. It explicitly distinguishes itself from the sibling cairn_a2a_card, which 'already saves the first one', so an agent can route correctly without opening either 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?

Directly states the selection rule: use this one to update the card, while cairn_a2a_card handles the initial save. That is an explicit when-to-use plus a named alternative, leaving nothing to inference.

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