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

Annotations already carry readOnlyHint=false and idempotentHint=true. The description adds meaningful context: the data is self-reported planning, not assessed work, and retries with identical input are safe. It also implies optimistic concurrency via 'latest revision' without contradicting annotations.

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 short sentences, each serving a purpose: action, boundary, and operational requirement. Information is front-loaded and there is no filler.

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 mutating tool with idempotency and an output schema, the description covers the key operational details (revision, requestId, ownership, self-reporting). It doesn't spell out stale-revision failure behavior, but 'latest revision' and safe retry language imply it; this is adequate given the annotations.

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 only 25%, so the description must compensate. It adds meaning for requestId (unique, retry-safe) and expectedRevision (latest revision), but planId semantics are only implicit in 'owned plan tasks' and the tasks array structure is left to the schema. Partial compensation for the coverage gap.

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 opens with a specific verb ('Marks') and resource ('owned plan tasks'), and clarifies the action is toggling completion status. It explicitly distinguishes itself from quiz scoring/practice submission, separating it from sibling tools like submit_practice_answer and check_practice_answer.

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 the intended context ('at the student's request') and a firm exclusion ('never a quiz score or practice submission'), which tells an agent when not to use it. It also provides usage prerequisites (latest revision and unique requestId) though it does not explicitly name alternative sibling tools.

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