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

Annotations already cover the safety profile (readOnly, idempotent, not destructive/open-world), but the description adds real behavioral value: the failure mode ('An unknown id returns not-found rather than a guess') and the conditional return fields ('where one was given'), which tells the agent optional data may be absent.

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?

Three tight sentences, front-loaded with what is returned, then usage, then the identifier-only constraint and error behavior. No filler and nothing redundant.

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 compensates by listing the returned fields and noting they are conditional, and it documents the not-found behavior. For a single-parameter, read-only lookup, an agent has everything needed to call it correctly.

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 gives the id description and an example. The description reinforces that the tool takes an id and nothing else, but adds no format, naming, or lookup semantics beyond what the schema provides, so the baseline of 3 applies.

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 (retrieve) plus resource (one community) plus the identity key (directory id), and it enumerates what comes back (join link, platform, region, topic, member count). It is clearly distinguishable from search_communities, which discovers rather than fetches.

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?

Explicitly states both when to use it (answering a specific question about one group, or filling in join links after search_communities) and when not to (discovery), plus the ordering rule 'Search first.' The alternative is named and the selection condition is unambiguous.

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