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

Annotations already declare readOnlyHint=true and openWorldHint=false, but the description adds substantial context: the data is federally-sourced and audience-safety-checked, the tool does not enumerate messages (corpus stays internal), and it references a catalog for gating contracts. This goes well beyond what annotations provide.

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 sentences, each with a distinct purpose: core function, use case, and exclusions/alternative pointer. No redundancy or unnecessary detail; it is front-loaded with the primary action.

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 simple zero-parameter, read-only tool with an output schema, the description covers what it returns, when to use it, what it does not return, and where to find more information. It is entirely sufficient for an agent to select and invoke 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?

The tool has zero parameters, and the input schema is empty with additionalProperties=false. Per the rubric, 0 parameters earns a baseline of 4. The description adds no parameter-level details because none exist, which is appropriate.

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 uses the specific verb 'List' with a clearly defined resource ('curated sandbox topic labels that define the free Discovery corpus'). It distinguishes itself from sibling tools by explicitly stating that it previews content domains before creating a stream, rather than managing streams or messages.

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?

It states exactly when to use the tool: 'Use it to preview what content domains exist before creating a stream.' It also provides an explicit exclusion ('Does NOT enumerate messages') and directs the user to an alternative resource ('signal://catalog resource') for more comprehensive template and gating information.

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