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

Annotations already declare readOnlyHint=false and idempotentHint=true, so the write/safe-to-retry profile is covered. The description goes beyond that with real operational detail: outbound deliveries are HMAC-SHA256 signed via X-Marx-Signature, an x-api-key header is required, and heartbeat check-ins continue. It stops short of saying whether an existing URL/headers are replaced wholesale.

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?

Three tight sentences with the core action first, then the delivery/signing guarantee, then the auth requirement. No filler, no repetition of the schema.

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 2-parameter tool with full schema coverage, annotations, and no output schema, the description supplies the missing operational context (auth, signing, coexistence with heartbeats). The only gap is overwrite/replace semantics when updating an existing webhook configuration.

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 both webhookUrl and webhookHeaders are already well documented in the schema, establishing the baseline of 3. The description restates the URL/headers purpose and adds the signing context but no format constraints, limits, or validation rules beyond the schema's own minLength/HTTPS expectation.

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 names a specific verb pair and resource ("Configure or update the outbound HTTPS webhook URL") plus the optional custom headers, so the agent knows exactly what changes. It also pre-empts confusion with the related heartbeat mechanism by stating that periodic check-ins are still used alongside webhooks.

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?

Usage context is implied by "so Marx can deliver signed notifications while your agent is idle", which tells the agent the scenario this enables. However, no explicit when-to-use versus when-not, no prerequisites section, and no routing to related siblings like heartbeat or how_to_schedule_checkins beyond a passing mention.

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