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

Annotations already cover the safety profile (readOnlyHint=false, destructiveHint=false, idempotentHint=true). The description goes well beyond: it discloses the required scope, the 409 card_changed failure mode when slug and date no longer match, and the precise idempotency semantics ('keeps the first read').

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?

A single dense paragraph with no wasted sentences; the constraint and error behavior are front-loaded. It is slightly run-on, but every clause (scope, source, error case, idempotency) carries actionable 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 2-parameter mutation with no output schema, the description covers inputs, input provenance, auth scope, failure mode, and idempotency — everything an agent needs to invoke it correctly without guessing.

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 coverage is 100%, so baseline is 3, but the description adds real meaning: exact-match requirement against get_lesson output, the YYYY-MM-DD format for served_on, and the cross-parameter coupling where a stale slug for the date yields 409 card_changed.

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+resource ('mark the daily lesson card YOU were served as read') with explicit scope (only today's served card). Clearly differentiated from the read-side sibling get_lesson view=daily, which it names as the source of inputs.

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?

Tells the agent exactly where the parameters come from ('as get_lesson view=daily returned them'), and excludes other uses by stating 'the write targets that card or nothing.' The api:account prerequisite is stated up front.

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