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

The description discloses important behavior beyond the readOnlyHint annotation: it returns newest-first, mail may take seconds to arrive, calls are non-blocking, and an empty response means retry. It also warns that text view flattens away layout and branding, which is crucial for auditing use. This is rich, non-obvious behavioral context.

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 longer than average, but every sentence serves a purpose: purpose, ordering, retry behavior, and format semantics. It is front-loaded with the core action and provides details in a logical order. Slight verbosity keeps it from a 5, but it is well-structured.

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?

Given no output schema, the description does a good job of explaining what to expect (newest-first messages, empty responses) and what to do next (extract code/link, audit with html). It lacks an explicit response structure, but for this simple read operation the agent has enough context to proceed confidently.

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 beyond the schema by explaining format='text' versus 'html' in practical terms (read code vs audit layout, write to file, screenshot) and by emphasizing that address and inbox_token come from create_inbox. This helps an agent use parameters correctly.

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 a specific verb and resource: 'Read mail delivered to an inbox from create_inbox.' It immediately distinguishes the tool from siblings by tying it to the inbox lifecycle and gives concrete use cases (verification codes, confirmation links). No other sibling reads mail, so this is clearly differentiated.

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 gives explicit operating guidance: when the response is empty, wait and retry; there is no blocking wait; use format="html" specifically for auditing emails, while text is for extracting codes. This effectively tells the agent when and how to use the tool, including the conditional for the format parameter.

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