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

With readOnlyHint=false, an agent would otherwise be puzzled why a 'read' tool is flagged as a mutation; the description resolves this by stating 'Marks it read.' It also discloses the enriched return payload (verification codes, ranked links), which matters since there is no output schema. Missing only edge-case behaviour such as what happens when the id is unknown.

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?

A single sentence with zero waste: the action and target lead, the payload inventory follows, and the side effect is placed last where it reads as a caveat. Nothing is padded or repeated from the schema.

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 two-parameter reader with no output schema, the description covers the return shape, the optional format choice, and the read-marking side effect. It stops short of error/not-found behaviour and any auth or rate-limit context, which are the only notable gaps.

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 both parameters are already documented in the schema, including the format enum. The description's 'optionally sanitised HTML' echoes the format parameter but adds no format syntax or default detail beyond it, so baseline 3 applies.

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?

States a specific verb and resource ('Read one email') and enumerates exactly what is returned (sender, subject, text, HTML, verification codes, ranked links, attachments). That content scope clearly separates it from the sibling list_emails/wait_for_email tools, which cannot return a single fully-parsed message.

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?

Usage is only implied: the required email_id signals 'use when you already have a message id'. There is no explicit when-to-use, no when-not-to-use, and no pointer to sibling tools such as list_emails for discovery or search for locating an id.

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