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

Annotations already declare idempotentHint=true and the safety profile, so the bar is lower. The description still adds concrete value by explaining the no-op behavior on repeated reactions and disclosing the API key requirement, an auth detail annotations don't cover.

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?

Three tight sentences, front-loaded with the core action, then the edge-case behavior, then the prerequisite. No filler and every sentence carries required information.

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 simple two-parameter mutation with a self-documenting schema and no output schema, the description covers the action, idempotency, and auth requirement. Only the return shape is unstated, which is a minor gap given no output schema exists.

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 description coverage is 100% and the enum of reaction types is fully documented in the schema, so the description carries no extra parameter burden. It adds nothing beyond what the schema already states, making the baseline 3 correct.

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 (Add) and resource (reaction to an article), so an agent immediately knows what it does. It implicitly contrasts with the remove_reaction and get_reactions siblings, but never names them, so differentiation is left to inference.

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 by the action name and the 'No-ops if already reacted' note, but there is no explicit when-to-use or when-not-to-use guidance. It doesn't clarify, for example, when to call remove_reaction instead, leaving the agent to infer the pairing.

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