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

Annotations declare readOnlyHint and openWorldHint, so with that lower bar the description still adds genuine value: it discloses that the data is cached and best-effort, that counts are approximate, and that a 'last-checked' timestamp exists, which tells the agent the data may be stale. It doesn't mention refresh behavior or failure modes when a hostname is unknown.

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 tight sentences, fields front-loaded, no filler. The 'Input is the PDS hostname' clause partially restates what the schema and the parameter's own example already say, which is minor redundancy but not bloat.

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-value explanation is not strictly required, yet the description still names the payload contents helpfully. Combined with the caching caveat and a 100%-covered single parameter, an agent has enough to call this correctly; only the sibling-differentiation gap keeps it from a 5.

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% for the single hostname parameter and the description merely repeats the same example (pds.example.com). No additional meaning, format constraints, or edge-case handling is added beyond the schema, so the baseline 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?

States a specific verb+resource ('cached health card for a PDS from pds.directory') and enumerates the returned fields (version, DID, user count, reachability, last-checked, domains, relays). It is clear what the tool does, though it never distinguishes itself from the sibling describe_pds, which an agent will likely confuse it with.

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 description explains what the input is but gives no when-to-use guidance, no prerequisites, and no exclusions. With a sibling named describe_pds that sounds functionally adjacent, the absence of any routing cue ('use describe_pds instead when X') leaves the agent to guess between them.

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