get_messages_summary

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

Despite having no annotations, the description thoroughly discloses behavioral traits: it is non-mutating ('Never marks messages read'), it decrypts on the fly when RELAY_ENCRYPTION_KEY is set, it requires agent token auth (own mailbox only), and it notes the since filter nuance with 'ALREADY-OBSERVED history' and the PENDING drain behavior. This fully covers the behavioral burden, exceeding what annotations would typically 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?

The description is well-structured with clear sections: purpose, when-to-use, behavior, returns, and errors. It is informative yet concise, with no redundant sentences. Every sentence adds value (e.g., the content_truncated flag explanation, error codes). The formatting with headers aids readability and scannability.

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 preview tool with 5 parameters, the description is complete: it covers the tool's purpose, usage scenario, behavioral nuances (including tricky since semantics), return format, auth requirements, and error codes. There is no output schema, so the return structure detail is valuable)Skip, and the description fully compensates for the lack of structured output metadata. It is comprehensive enough for an agent to correctly invoke and interpret results.

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%, so the schema already documents all parameters with detailed descriptions, including the complex 'since' semantics and status filter. The description adds a brief note about the same status/since surface as get_messages, but it doesn't go beyond what the schema already explains. Baseline 3 is appropriate since the schema carries the load.

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 it is a cheap, non-mutating mailbox preview. It distinguishes itself from siblings by explicitly mentioning get_messages as the mutating alternative, and the return structure provides concrete specifics. The verb 'preview' plus the resource 'mailbox' makes the purpose unambiguous.

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 explicitly states when to use: 'orchestrators scanning many inboxes per cycle, dashboards rendering backlog count, or any flow where you want to see what is there without consuming it.' It also provides a clear alternative: 'After picking interesting IDs, expand them with get_messages (which CAN mutate) or read them by ID.' This gives both positive and negative usage context.

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