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

Annotations already declare the mutation profile (readOnlyHint=false, destructiveHint=false, idempotentHint=true), so the bar is lower. The description still adds real behavioral context beyond them: the call counts toward the user's daily streak and is equivalent to finishing in the app. It does not say what the response contains (e.g., updated streak count), which is a minor remaining gap.

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 sentences, front-loaded with the action and its effect, then the precondition. Every clause carries information; nothing is redundant.

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 zero-parameter action tool with annotations covering safety and idempotency, the definition gives enough: what it does, the gating condition, and the streak side effect. The only missing piece is what the call returns, but with no output schema and a short action, that omission is small.

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?

There are zero parameters, so the baseline is 4. The description correctly implies no arguments are needed and that the target feed is implicit ("today's" feed), which matches the empty schema.

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 uses a specific verb and resource ("Mark the user's daily Reulay feed as done") and explicitly ties it to the sibling tool that produces the feed (get_today_feed). An agent can distinguish it from read-only siblings like get_today_feed or play_feed_video without opening any schema.

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?

It states a hard precondition ("Only call this when the user has actually finished the feed") and names the upstream tool whose output gates the call. Both when-to-use and when-not-to-use are explicit, leaving nothing to inference.

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