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

Annotations already declare the write/destructive/idempotent profile, and the description adds genuinely non-obvious context: setting a signature marks its source as 'manual' and permanently overrides Gmail auto-import for that inbox, the missing text/HTML half is derived on send, and signature_enabled=false stops appending without deleting the text. These side effects are not derivable from the annotations or schema.

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 primary action and the two main signature fields are front-loaded, and most clauses carry distinct information (clearing, defaults, override behavior). It is a dense single paragraph, and the sender_name example restates schema text almost verbatim, so a little trimming is possible.

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?

Every parameter is addressed, defaults are stated, the clear-via-empty-string convention is repeated for each field, and the permanent Gmail auto-import override is disclosed; the output schema covers return values so it need not. Nothing material for a correct call is missing.

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 baseline is 3, but the description adds real semantics: the automatic derivation between signature_text and signature_html, the 'clear' meaning of empty strings, and prose explanations of 'always'/'first_only'/'never' reply modes. The sender_name example largely duplicates the schema, which keeps this from a 5.

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 up front ('Set or update the email signature for an inbox'), which cleanly separates it from the only nearby sibling, signature_get. An agent can tell immediately this is the write counterpart to the getter without opening either 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?

Gives strong conditional guidance: pass either or both of signature_text/signature_html, empty string for both clears the signature, and sender_name can be set on its own without touching the signature. It never names an alternative tool (e.g. signature_get) or states when not to call this, so it stops short of explicit routing.

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