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

Beyond the annotations, the description discloses important behavioral traits: it shows a QR code in chat, it is idempotent (if already linked, it says so), and it warns that Zalo allows only one linked web session and may terminate another session. This is valuable context for a connection tool that mutates external state.

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?

The description is compact and front-loaded: it opens with the purpose and location of the QR code, then gives the exact user steps, followed by post-conditions and a critical caveat. Every sentence carries useful information without repetition.

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?

For a no-parameter, interactive connection tool with an output schema, the description is complete. It covers what the tool does, how to use it, what happens after success, what happens if already linked, and the main risk (single-session limitation). Nothing essential is missing.

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?

The tool has zero parameters and the schema coverage is 100%, so there is no parameter semantics for the description to add. The baseline for zero-parameter tools is 4, and the description appropriately focuses on the interaction flow rather than inputs.

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 states a specific verb and resource: "Link Zalo to Local MCP by showing a QR code right here in the chat." It clearly differentiates this from the other Zalo tools (list/search/send/disconnect) by explaining it is the connection/setup step, and it names the tools that will start working afterward.

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 explicit step-by-step instructions: call this tool, open Zalo on the phone, use the QR-scan option, and scan. It also says the Zalo tools start working after scanning, which tells the agent when this tool is the right prerequisite. It does not explicitly list when-not-to-use or alternatives, but the guidance is clear and actionable.

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