Plan and budget

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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), so the description's real contribution is 'Needs TILLA_API_KEY' – an authentication prerequisite not captured by annotations, which is exactly the kind of context that matters. It also signals the data is current rather than cached, but says nothing about failure behavior if the key is missing or invalid.

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?

Two short clauses with zero filler: the return contents come first, the auth prerequisite second. Every phrase carries information an agent needs.

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?

With no output schema, the description correctly takes on the job of naming the returned fields, and with zero parameters and full annotation coverage there is little else required. It could still note the response shape or units (how 'limits' and 'used today' are expressed) for an agent that needs to parse the result.

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?

The tool takes zero parameters, so there is no parameter semantics to explain and the baseline of 4 applies. The description does not waste words on arguments, which is appropriate.

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 resource ('the caller's plan and budget right now') and enumerates exactly what it returns: tier, history days, limits, used today. That field list separates it from siblings like tilla_tiers (presumably a tier catalogue) and tilla_status, though no sibling is named explicitly.

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 is only implied: the mention of 'limits' and 'used today' suggests a quota/headroom check, and 'right now' implies a freshness-sensitive call. There is no explicit when-to-use, no when-not-to-use, and no routing to tilla_tiers or tilla_status as alternatives.

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