Get a contact

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

Annotations already declare readOnly, idempotent, non-destructive, and openWorld, so the safety profile is covered. The description adds genuinely useful context beyond them: the read is against the channel's local contact store and does not hit WhatsApp, which tells the agent the data may be stale/incomplete compared to a live lookup.

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 core action, then the scoping caveat, then the parameter format. Two compact clauses with no filler; only minor density in the parenthetical.

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?

With no output schema, the description usefully notes the entry is the names the contact store holds, so the agent knows roughly what comes back. It omits what happens when the contact is absent from the store (null vs error), a small remaining gap for a single-param read tool.

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 says 'a user JID or a LID', but the description adds a concrete format example (15551234567@s.whatsapp.net), which materially helps the agent construct a valid 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+resource ('read this channel's stored entry for one contact') and immediately scopes it as the local contact store rather than a live WhatsApp lookup. This distinguishes it from the sibling chat/message/group tools, which all operate on other resources.

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 implies the use case (resolve a stored contact entry locally) and rules out the WhatsApp-query interpretation, but it names no alternative tool and gives no explicit when-to-use/when-not-to-use condition beyond the 'does not ask WhatsApp' scope note.

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