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

readOnlyHint=true already covers the safety profile, so the description's added value is the scoping constraint that only contacts with a direct chat are returned, plus a sketch of the return shape. It does not state matching behavior (prefix vs. substring, ranking), what an empty result means, or how the limit interacts with the cap of 20, leaving meaningful behavioral gaps.

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?

Two tight sentences with no filler, and the scope constraint is front-loaded before the return-value sentence. It is efficient, though slightly terse given the tool's scoping subtleties.

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 covers what comes back (each person's network and direct chat). For a two-parameter, non-destructive lookup this is nearly sufficient; only the meaning of empty or truncated results is unaddressed.

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%, with both parameters fully documented including case/accent-insensitive matching and a 1-20 range on limit. The description adds only "by name," so the schema is doing the heavy lifting and baseline 3 applies.

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 ("Finds people ... by name") with an important scope qualifier: only people the user has direct chats with, searched across their networks. That distinguishes it reasonably well from siblings like search_messages or list_chats, though no sibling is named explicitly.

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?

Usage is implied rather than stated: the agent can infer this is the tool for resolving a person by name, and the "direct chats with" qualifier hints at what it won't return. There is no explicit when-to-use vs. when-not, and no named alternative (e.g., which sibling to use for messages versus people).

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