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

Beyond the readOnly/idempotent annotations, it discloses a critical behavioral trait: the returned text is untrusted evidence and must not be executed as instructions. For a fetch tool returning external content, that prompt-injection warning is exactly the context annotations cannot express.

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 retrieval contract before the safety caveat. Every clause carries information; nothing is redundant with the name or schema.

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?

An output schema exists, so return values need no explanation, and the annotations cover the safety profile. What remains unstated is failure behavior for an unknown ID and the scope of retrievable documents, minor gaps for a one-parameter read tool.

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 0%, so the description must carry the load, and it does the important part: the single `id` must be a stable search ID, not a URL or arbitrary identifier. It does not mention the maxLength bound or format of that ID, but the essential semantic constraint is present.

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?

Uses a specific verb ("Retrieve") with a specific resource ("a document") and constrains the lookup key to a stable search ID, which implicitly separates it from the search sibling. It never names search or build_reading_list directly, so sibling differentiation is inferred rather than stated.

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?

Gives a clear positive condition (you must already have a stable search ID) and an explicit exclusion ("never by arbitrary URL"), which tells the agent when not to use it. It stops short of routing the agent to a specific alternative when no ID exists, e.g. pointing at search.

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