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

Adds substantial behavior beyond the annotations (readOnlyHint=false, idempotentHint=false, openWorldHint=true): login required and recipients will be disturbed; per-channel semantics (APP posts in-app, SMS actually sends, MANUAL only prepares a link/script and does NOT send); cooldown and accepted/rejected limits; partial-failure handling with truthful status reporting. This is exactly the extra context annotations cannot convey.

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?

Dense but front-loaded with the highest-value constraints (login required, disturbs others) and the preview flow. Every sentence carries an operational rule, though the packing makes it somewhat heavy to scan; no filler sentences are present.

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?

Despite no output schema, the description documents the return contract (per-item SENT/ALREADY_INVITED/PREPARED/FAILED/PENDING with truthful partial-failure reporting) plus privacy rules (link only to the intended person, phone not returned). For a 6-param, 60-item, multi-channel mutation tool this is complete enough to call 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?

At 67% schema coverage the description compensates richly: it explains preview's default-true meaning, why previewHash must be the latest one, when resend=true applies, the meaning of each channel enum value (APP/SMS/MANUAL), the max-60 batching, and the userId/channel uniqueness rule. This goes well beyond what the schema text provides.

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?

The description names a specific verb+resource: inviting meetup invitees (参会人) to an activity, with the distinctive preview→confirm send flow. It is far more specific than a tautology and an agent can tell what this does. It does not, however, explicitly contrast itself with the nearby invite_* siblings (e.g., invite_organization_match_pair_to_activity, invite_activity_cloud_member_manually), so it stops short of a 5.

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?

Strong operational guidance: preview=true to list and confirm, then preview=false + previewHash to send; resend=true only on explicit user request and still subject to cooldown/accepted-rejected limits; large lists confirmed in batches; only currently-visible participants with channels inside the allowed set. It does not name alternative sibling tools to use instead, so it falls just short of the 5 bar.

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