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

With only destructiveHint=true provided, the description adds real value: it flags the call as a WRITE, discloses that no SMS is sent, and warns that update=true overwrites firstname/lastname/custom1-3. It stops short of stating auth requirements or the handling of fields omitted during an update.

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-loads the 'WRITE:' marker and the core action, then adds only the constraints an agent needs. Slightly dense/run-on in the middle clause, but every sentence carries information.

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 9-parameter mutation tool with no output schema, it covers the essential edge cases (opt-out, no-SMS side effect, overwrite behavior on update). It leaves subaccount semantics and non-update parameter behavior to the schema, which is a minor gap.

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 only 44%, so the description must compensate. It clarifies the role of mobile, group and update and gestures at the name/custom fields, but firstname, lastname, custom1-3 and subaccount still lack any description-level meaning. Partial compensation for the coverage gap, landing at the baseline.

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 ('adds a contact (by mobile number) to the FireText account') with the dual mode spelled out ('or with update=true refreshes the names/custom fields'). The 'Does not send any SMS' clause cleanly separates it from firetext_send_sms, so an agent can route without opening the 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?

Explains the conditional use of update=true and states the important exclusion that opted-out contacts cannot be re-added this way. It gives clear context but never names a sibling tool (e.g. unsubscribe_contact) as the alternative path, so it stays just short of explicit when/when-not routing.

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