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

Annotations already flag destructiveHint=true and idempotentHint=false, and the description adds meaningful extra context: it sends immediately, consumes sending credit, and cannot be recalled. That is real value beyond structured fields, though it stops short of covering failures, rate limits, or verified-sender rejection behavior beyond what the schema notes.

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?

Front-loaded with the action and scope, then constraints, then the guardrail and exclusion. Nearly every clause carries a distinct operational fact; there is no filler.

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 10-parameter mutation with no output schema and a nested merge_tags object, the description covers the highest-risk decisions (mode selection, credit cost, irreversibility, user confirmation). Only minor gaps remain, such as reply_to semantics and what a success response contains.

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 60%, so the description partially compensates by adding the critical constraint the schema does not encode: give html OR template_id, not both, and merge_tags must cover every tag in the template. That prevents a real invocation error; reply_to params remain unaddressed but are optional and self-named.

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?

Opens with a specific verb and scope: 'send a single one-to-one email to one recipient through Mail Blaze.' Explicitly contrasts with campaign/bulk paths, so the agent can separate it from mailblaze_create_campaign without opening a schema.

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?

States the negative case ('Not for bulk or marketing mail; use a campaign for that') and names the alternative. Also adds a procedural gate: 'Confirm the recipient and content with the user before calling.' Both when-not and a prerequisite are explicit.

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