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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint=false and destructiveHint=false. The description still adds real value: 'Efectos secundarios: ninguno (solo lectura, sin red, sin estado guardado)', determinism ('la misma entrada da la misma salida') and concrete limits (64 KB input, 1 s, 1 MB result) that no annotation carries.

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?

The content is labeled and front-loaded (purpose, when, not-for, side effects, limits), but the Spanish block is duplicated by a deferred 'full EN: inputSchema.description' pointer, and the 'Límites: 64 KB JSON / 1 s' boilerplate plus the off-topic 'Cuándo' sentence cost space without earning it.

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 an output schema present and 100% param coverage, the core contract is covered. The remaining gap is that the when-to-use sentence points at document/receipt parsing rather than at cost/budget scenarios, and the English text lives only behind a pointer into inputSchema.description, so the definition is adequate but not self-sufficient.

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 all four parameters are documented in the schema and baseline is 3. The description adds modest semantics — 'after a free allowance' explains free_calls and 'Exact decimal math' justifies the string-typed price/budget fields — but nothing about the budget_usd/calls interaction that the schema does not already imply.

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 opening sentence names a specific verb and resource: estimate the cost of a batch of pay-per-call requests, reported in USD and USDC base units, including budget coverage. It also names the sibling it is not (llm-cost-estimate). The following 'Cuándo' clause is about reading/converting OpenAPI docs and receipts, which is unrelated to cost estimation and dilutes an otherwise clear purpose.

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 explicit exclusion 'No para: estimar el costo de llamadas a un LLM a partir de tokens (llm-cost-estimate)' is a genuine routing signal. However, the positive 'Cuándo' guidance describes parsing a document or receipt, which does not match what the tool does, so the when-to-use half is misleading rather than helpful.

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