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

readOnlyHint=true already establishes the safety profile, and the description adds real context on top: results are filtered to active custom signatures, scoped to the authenticated user, and ordered newest first. It does not mention pagination, result caps, or what happens when the user has no signatures, which is the only remaining gap.

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 short sentences with zero waste — what it returns is front-loaded, and the downstream usage note follows. Every clause carries information.

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 zero-parameter read-only list with no output schema, the description covers the essentials: what is listed, the filter, the ordering, and how to use the result. Only pagination behavior and the shape of a signature record are unaddressed, which are minor for a simple lookup.

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 takes zero parameters, so there is nothing for the description to disambiguate; baseline 4 applies. The mention of signature_id is a downstream field of another tool, not a parameter of this one.

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 gives a specific verb and resource ('List active custom signatures') plus scope ('available to the authenticated user') and ordering ('newest first'). No sibling tool lists signatures, so an agent can immediately tell this apart from the postcard and account tools.

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?

'Use an ID from this list as signature_id when creating a postcard' explicitly chains this tool to create-postcard-tool, which is a genuine when-to-use instruction. It stops short of naming any exclusion or stating when not to call it, which keeps it out of 5 territory.

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