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

Annotations already declare this is not read-only, not idempotent, and not destructive, so the mutation nature is clear. The description adds useful setup context by enumerating the return payload (webhook URL, config set, topic names, remaining steps) and notes that retention is configured elsewhere in the web UI, which is a behavioral constraint not visible in the 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?

Two sentences with no redundant information. The primary action and return format come first, and the retention note is placed at the end as a clarifying aside.

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?

With annotations, full schema coverage, and an output schema present, the description need not explain return values, yet it helpfully summarizes the wiring details provided. The only gap is that it doesn't clarify prerequisites or when to use this versus updating an existing source, but that is minor for a creation tool.

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 both parameters thoroughly (name as display name, color as badge with default). The description adds no syntax or meaning beyond what the schema provides, so baseline 3 is appropriate.

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 (create) and resource (email source), and immediately constrains the scoping ('one per app or mail stream'). It also describes what the tool returns, which distinguishes it from the sibling get_source_setup, which presumably only retrieves wiring for a pre-existing source.

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 implies usage by saying it returns AWS SES wiring details, but it never explicitly says when to use create_source versus alternatives like update_source or get_source_setup. An agent must infer that this is for initial setup only.

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