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

Annotations already declare readOnly/idempotent/non-destructive/closed-world, so the safety profile is covered. The description adds real behavior beyond that: unknown slugs return course_not_found, price is always free with a service level and replacement policy, and content.available signals whether module text can be fetched here.

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, zero preamble, with the use case and the error behavior front-loaded. The second sentence is a long comma-chained field list that is dense but each item is informative; it could have been trimmed slightly given an output schema exists.

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?

Covers the discovery question, the single required parameter's failure mode, and the availability gate for downstream module tools. Enumeration of return fields is partly redundant since an output schema exists, but the extra behavioral notes (free price, replacement policy, content.available) make it complete enough for a one-param lookup.

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% and the schema already documents slug and its listCourses provenance, so the baseline would be 3. The description adds parameter-level error semantics — an unknown slug yields course_not_found — which is meaning the schema does not carry.

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?

Specific verb+resource: retrieves the pedagogical record for one course identified by slug, and enumerates the fields it exposes (level, duration, prerequisites, eligibility, price, URL). Sibling differentiation is only implicit — it hints that module text lives behind other tools ('whether module text is retrievable here ... and the tools') but never names getCourseModules/getModuleContent or listCourses.

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?

Front-loads the decision context ('Use to decide whether a course fits a learner'), which tells the agent when this tool is the right one. It stops short of explicit exclusions — it does not say to use listCourses for discovery or getModuleContent for the text — so the boundary with siblings is inferred rather than stated.

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