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 value beyond that by describing the returned sections and the non-obvious conditional: action fields are empty when the value follows an underlying cause. It does not cover language fallback or unknown-slug behavior.

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?

Front-loaded with the purpose, then a single dense but purposeful sentence enumerating returned content. The clause about empty action fields is slightly convoluted but earns its place by preventing a misread of an empty result.

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?

With no output schema, the description correctly carries the burden of explaining return content and even an edge case in the payload. Minor gaps remain: no mention of the lang default's effect on output or error behavior for an unknown slug.

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%, with both slug and lang fully documented including the canonical slug examples and enum values, so baseline is 3. The description mentions the slug input but adds no new semantics such as slug normalization or what 'lang' affects in the response.

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 and resource ('Return the full explainer for a single blood-test marker by slug') and enumerates the content, so the agent knows exactly what it gets. It does not explicitly distinguish itself from nearby siblings like mediora__lookup_marker or mediora__get_test_details, which likely also take a slug.

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 only implied: 'by slug' hints this is the deep-detail call, but there is no statement of when to prefer it over lookup_marker or get_test_details, nor any exclusion. Slug discovery guidance lives in the schema, not the description, so the routing logic is left to inference.

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