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

Annotations already declare the non-read-only, non-idempotent, non-destructive, open-world profile; the description adds the details that actually matter for calling it safely — keys are returned once and cannot be re-fetched, and signups are throttled to 5 per hour per network. That one-time-secret disclosure is critical operational context an agent could not infer from 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?

Three tight sentences: what it does, what it returns plus the store-the-keys warning, then the rate limit. No filler and the most actionable warning is not buried.

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?

There is no output schema, and the description compensates by enumerating the four return values. Combined with the one-time-key warning, rate limit, and fully documented parameters, an agent has everything needed to invoke and handle the result correctly.

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 100%: all three required parameters carry their own descriptions including format constraints and the hashing note. The description adds no parameter-level meaning beyond the schema, so baseline 3 applies.

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 ("Sign up an API for API Meter") and immediately names the concrete outputs (slug, ingest key, dashboard key, proxy URL). None of the siblings (export_usage, get_ingest_snippet, get_usage) create accounts, so the agent can tell this is the only write/provisioning path.

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 free-tier boundary ("free to 250K requests/month") and the network rate cap give the agent clear context for when this call is appropriate and what volume it implies. There are no exclusions or named alternatives, but no sibling overlaps this capability, so routing is unambiguous.

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