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

Annotations only declare readOnlyHint=true; the description goes well beyond by disclosing exact output fields, the masking rule ('a full identifier is NEVER returned'), the cited policy SEC-PM-006, and the auth prerequisite. That is precisely the behavioral context annotations cannot carry.

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 short paragraphs, output shape front-loaded ahead of the access requirement. Every sentence earns its place, though the parenthetical example phone could be trimmed slightly.

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 compensates by naming the returned fields (has_telegram/has_whatsapp, enrolled_phone_hint) and the masking constraint, plus the auth requirement. An agent has everything needed to call 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?

Only one parameter (id) and schema coverage is 100%, so the schema already documents the Circle ID pattern. The description adds nothing about the id beyond what the schema states, making the baseline 3 appropriate.

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 ('List a Circle's members') and immediately enumerates what each returned member contains. It is easy to distinguish from list_circles or list_circle_member_channels, though it never names those siblings 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?

Gives a concrete prerequisite (Proof account required, re-authenticate via /mcp in Claude Code) and explicitly rules out a tempting alternative path ('start_login does NOT open this tool'). It does not, however, say when to prefer it over a filtered member lookup, so it stops short of full when/when-not routing.

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