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

Annotations already declare readOnly, idempotent and openWorld, so the safety profile is covered. The description adds meaningful behavior beyond that: pricing per call and the x402 payment handshake, including that the tool returns payment requirements unless payment_signature is supplied. That is genuinely useful operational context not present in the 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?

Dense but front-loaded: purpose first, then usage trigger, then pricing/payment mechanics, then a sample pointer. Every clause carries information, though the pricing and sample tokens add minor clutter for an agent whose main job is selection.

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 takes on the burden of describing returns and does so ('returns the x402 payment requirements unless payment_signature is given'). Combined with full schema coverage and read-only annotations, an agent has enough to call it correctly, though result shape (fields per grant call) is still unspecified.

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 five parameters are already documented with defaults and semantics (limit range, status values, payment_signature relay, min_days_to_deadline). The description adds nothing parameter-specific beyond the payment flow already covered, 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 ('Find open or upcoming EU grant calls') and scopes it to a topic fit, which separates it from sibling search tools like search_tenders or search_us_federal_awards. An agent can identify what it returns 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?

Gives an explicit triggering context ('Use when scouting Horizon Europe, Digital Europe, LIFE, CEF, EU4Health or similar funding'), which tells the agent when this tool is the right pick. It stops short of naming exclusion conditions or an explicit alternative sibling for non-EU procurement, so it is clear but not exhaustive.

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