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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), but the description goes further with billing behavior ('does not consume a score and is not billed'), session semantics ('anonymous cap...can reset on rotating egress'), and key-scoping rules ('a tw_ key does not select this cap'). This is meaningful context the annotations cannot express.

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 core purpose, then usage, then exclusions, then parameter nuance, then return scope. Dense but each sentence carries distinct information; only the api_key restatement is mildly redundant with 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 one-parameter read tool with no output schema, the description is complete: it names the return ('remaining SpendGate count only'), the billing and session caveats, and the routing to sibling quota tools. Nothing an agent needs to call it correctly 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 coverage is 100%, so baseline is 3, and the description adds genuine meaning: what kind of key api_key expects (sg_live_), what happens when omitted (anonymous IP/session cap), and its rotation caveat. It slightly restates the schema's own api_key description, which keeps it 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 (read the remaining free SpendGate score count for this caller) and immediately distinguishes itself from the look-alike quotas in sibling tools (Toolweather health-check quota, paycheck_get_quota). An agent can identify the tool 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?

Explicit when-to-use ('before a run of score_spend calls') and explicit when-not-to-use, naming the three alternatives (Toolweather quota, paycheck_get_quota, key-minting tools). It even calls out which key type does not select this cap, leaving nothing to inference.

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