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

With no annotations, the description fully discloses behavior: retention (24h, 500 cap), default max 100, exclusive pagination semantics, free identity TTL extension, and response fields (`expires_at_iso`, `upgrade_hint`). This is exceptionally transparent.

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 compact yet dense, with no wasted words. It front-loads the purpose, then methodically adds pagination, retention, and lifecycle context. The structure is easy to parse and every sentence contributes new 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 3-parameter tool with no output schema, the description covers essential context: default behavior, limits, pagination, data lifetime, and special handling of free identities. It even hints at a prompt strategy (upgrade_hint). This is fully sufficient for an agent to 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?

Schema coverage is 100%, so the baseline is 3. The description adds value by explaining `since` as pagination from a specific message id (exclusive) and contextualizing the default limit and cap within the tool's behavior. It doesn't duplicate the schema; it enriches it.

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 opens with 'Read your DM inbox', a specific verb+resource combo, and clarifies scope with 'Returns messages addressed to your handle (free or paid).' It clearly differentiates from siblings like history or wait_dm by focusing on DMs and pagination.

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?

Provides clear usage context: pagination via `since`, default limit, retention window, and identity TTL extension. It does not explicitly exclude alternatives or mention when to prefer other tools, but the purpose is distinct enough that this is minor.

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