Read custom fields

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

Annotations already indicate `readOnlyHint: true` and `destructiveHint: false`, so the safety profile is established. The description adds meaningful behavioral context beyond those annotations: it reveals that the tool can access unregistered keys (a visibility limitation of `get_content`) and that a companion plugin is required for that capability. This helps the agent understand functional boundaries and dependencies, which annotations do not cover. No contradiction with annotations.

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?

The description is two sentences, front-loaded with the core action and resource, and every clause adds value. The contrast with `get_content` and the plugin requirement are both essential and concisely stated. No fluff or repetition; it is appropriately sized for the tool's complexity.

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?

For a read-only tool with 4 parameters (one required) and no output schema, the description covers the key functional distinction (access to unregistered keys), the dependency (companion plugin), and the primary alternative (`get_content`). The lack of an output schema means return format isn't described, which is acceptable. Minor gaps: no mention of error handling (e.g., what happens if the plugin isn't installed) or performance considerations, but these are not critical for successful invocation. Overall, the description is nearly complete.

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?

The input schema provides detailed descriptions for all four parameters with 100% coverage, so the baseline is 3. The description does not add additional meaning about parameters—it doesn't explain how `keys` filters results, what `include_protected` does beyond the schema, or how `site_id` selection works. While the description's mention of 'unregistered keys' loosely relates to `include_protected`, the schema already covers that. Therefore the description adds minimal parameter value beyond the schema.

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?

The description clearly states the action ('Read the custom fields') and the resource ('a content item'). It explicitly distinguishes itself from the sibling `get_content` by noting it can access keys not registered with `show_in_rest`, which is a precise differentiator. The added caveat about the companion plugin further clarifies the scope, making the purpose unambiguous and actionable.

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 implies when to use this tool: when you need meta keys that are not visible through `get_content`. It names the alternative (`get_content`) and the condition (keys not registered with `show_in_rest`). However, it does not explicitly state exclusion cases (e.g., 'use get_content when you only need standard fields') nor mention write counterparts like `set_content_meta`. The guidance is clear but could be more explicit in routing between tools.

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