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

Annotations only flag it as a non-read-only, destructive, non-idempotent, open-world write; the description adds substantial context beyond that: it is attributed to the agent rather than the person, the person can lock or rewrite it, visibility is limited to group-sharers, it is shown as a claim and never as instructions, and it is marked unverified with no owner. It also discloses the rate limit (20 changes/day), content restrictions (no links, emails or @addresses), and that an empty text clears the line — all consistent with destructiveHint=true.

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?

It is longer than most definitions (seven sentences) but front-loads the core action and each sentence carries distinct information about attribution, visibility, locking, rate limits, and clearing. It could be tightened slightly, but there is little filler.

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?

There is no output schema, so the description must carry the behavioral burden — and it does, covering attribution, visibility scope, owner controls, verification status, content rules, rate limits, and clear semantics. An agent has everything needed to call this 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 coverage is 100% and the schema already supplies the maxLength and an example, so the baseline is 3. The description nonetheless adds real semantics beyond the schema: forbidden content types (links, emails, @addresses) and the non-obvious behavior that sending an empty string clears the value.

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 ('Set the one plain line on your card') with the exact payload described ('text, up to 140 characters'). It also clarifies the audience and purpose ('so other people's AIs know what to send you'), which distinguishes it from siblings like card, whoami, or send_message.

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 this applies — describing yourself so other AIs know what to send, including the special case of having no owner yet. It does not, however, name any sibling tool or state when not to use this versus alternatives such as card or whoami.

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