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

The description goes well beyond the annotations by disclosing the exact fields returned (subject, sender, destinations, SES tags, event timeline), the 500-event limit, the events_truncated flag, and the recommended paging mechanism. There is no contradiction with the readOnly/idempotent/non-destructive annotations.

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 a single, information-dense sentence that front-loads the core action ('Fetch one email') and packs in field lists, limits, and follow-up guidance. It is efficient but somewhat heavy with parentheticals, which slightly reduces readability.

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?

Together with the annotations (read-only, idempotent) and the presence of an output schema, the description covers the tool's purpose, input provenance, return contents, limits, truncation behavior, and continuation strategy. Nothing important is left unexplained for an agent to invoke this tool 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%, and the parameter description already states 'SES message id from search_events results'. The tool description repeats this same context without adding new syntactic, format, or behavioral details about the parameter, so it adds no incremental value beyond the schema.

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 uses a specific verb ('Fetch') and resource ('one email by its ses_message_id'), clearly distinguishing it from sibling tools like search_events (which lists events) and email_stats. It immediately states the exact input needed and the scope of the operation.

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?

It explicitly says the id comes 'from search_events results' and instructs using search_events to page through additional events, giving clear practical usage context. However, it does not explicitly contrast with email_stats or list_sources, so a small gap remains in alternative guidance.

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