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

Annotations already declare readOnly/idempotent/closed-world, so the safety profile is covered. The description adds real value beyond that: it discloses the not-found contract ({"error": "not_found"}) and that replies are "live" and ordered, implying hidden or deleted content is filtered out. It stops short of saying whether reply lists are truncated or paginated.

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, verb-first, zero preamble. Every clause in the enumeration carries information (what fields come back, reply ordering, marked-answer presence), and the error case is confined to its own short sentence.

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 must carry the return shape and it largely does — including the error case. For a single-parameter read tool this is close to complete; only reply-count limits and per-reply metadata (author, timestamps) are left unstated.

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 slug's pattern and example are already documented in the schema, so the description only echoes the key without adding format or constraint detail. Baseline 3 applies where the schema does the work.

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 ("Returns one topic by its slug") and then enumerates exactly what a topic is composed of: title, about, status, opening post, ordered live replies, and the marked answer. That enumeration is what separates it from list_topics (many) and open_topic, which an agent can see without opening the schema.

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?

The single-slug framing implies it is the lookup path when the slug is already known, and the sibling list_topics supplies the obvious alternative, but the description never says so explicitly and lists no exclusions. Usage is inferable rather than stated.

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