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

The description adds valuable behavioral context beyond annotations: it explains that the tool returns JWT tokens and automatically sets authentication for the session. While annotations provide hints (not read-only, open world, idempotent, non-destructive), the description clarifies the authentication persistence behavior, which is crucial for understanding session management.

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 perfectly concise with just two sentences that each serve distinct purposes: the first explains the authentication mechanism and return value, the second describes the session behavior. Every word earns its place with zero redundancy or unnecessary elaboration.

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 an authentication tool with comprehensive annotations and full parameter documentation, the description provides good contextual completeness by explaining the authentication flow, token return, and session persistence. The main gap is the lack of output schema, but the description partially compensates by specifying 'Returns JWT tokens.'

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?

With 100% schema description coverage, the schema already documents all 4 parameters thoroughly. The description doesn't add any parameter-specific information beyond what's in the schema, so it meets the baseline expectation without providing additional semantic context about parameter usage or relationships.

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 clearly states the specific action ('Authenticate with email/phone and password'), identifies the resource (DUAL system), and distinguishes from siblings like dual_login_guest and dual_refresh_token by specifying the authentication method. It goes beyond the tool name to explain the authentication mechanism.

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 provides clear context for when to use this tool ('for subsequent API calls' and 'Sets auth automatically for this session'), establishing it as the primary authentication mechanism. However, it doesn't explicitly mention when NOT to use it or name alternatives like dual_login_guest for guest access or dual_refresh_token for token renewal.

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