L50 Marketplace Data

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

Annotations already cover read-only and open-world safety, but the description adds a genuinely important operational fact absent from structured fields: the call costs $0.05, billed in USDC on Base via x402. That payment prerequisite is the kind of thing an agent must know before invoking. It does not disclose failure behavior, latency, or whether the charge applies to failed calls.

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?

One dense sentence that front-loads the resource and scope, then lists outputs and pricing. Every clause carries information; the marketplace and currency enumeration is necessary for disambiguation. Slightly crammed, but nothing is wasted and nothing important is 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?

With no output schema, the description compensates well by enumerating what comes back (ranges, best buy/sell, profit, deals with links), and it discloses the payment requirement. For a 5-parameter tool with full schema coverage this is close to sufficient; it could say more about payment flow or error handling, but an agent can call it correctly as written.

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 every parameter already carries a description and the baseline is 3. The description adds only an indirect hint about fees ("best place to sell after fees"), which maps loosely to ebayFeePercent, and says nothing about how max, condition, or marketplaces shape the result. Adequate but not additive.

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?

Uses a specific verb ("Compare") with a named resource (one product's price) and enumerates the exact outputs: price range per marketplace, cheapest buy, best sell after fees, flip profit and margin, best deals with links. It also names the four marketplaces and the GBP currency, which distinguishes it from the single-marketplace siblings (ebay_market, vinted_search, reverb_search, poshmark_search).

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?

Implied usage is clear: this is the cross-marketplace aggregation tool, while siblings each hit one marketplace. It also documents the default marketplace set (ebay, vinted, reverb) so the agent knows poshmark is opt-in reference data. It stops short of explicitly saying "use ebay_market instead for a single-site search" or warning about when comparison is overkill.

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

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

Annotations already cover safety (readOnlyHint) and scope (openWorldHint), and the description adds genuinely new behavioral context: this is a paid call at $0.02, settled in USDC on Base via x402, and the data is 'live' rather than cached. It does not mention rate limits, latency or failure modes, which keeps it short of a 5.

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?

A single dense sentence with zero filler: the capability, the site scope, the returned metrics and the pricing model all appear in order of importance. Nothing is repeated from the schema or annotations.

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 compensates by enumerating return fields, and it discloses the payment requirement that an agent must handle before calling. The remaining gap is default/fallback behavior for the optional marketplace parameter.

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 only 33% (only cost is documented), so the description has to carry weight. It partially does: 'for one keyword' clarifies keyword as a single search term, 'on 8 eBay sites' frames the marketplace enum, and 'optional profit from your cost' explains the cost parameter. It never states the default marketplace when the parameter is omitted, leaving a real gap.

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?

Names the resource (live eBay market data for one keyword across 8 eBay sites) and enumerates the concrete outputs: price range with postage, seller concentration, China share, cheapest listings and optional profit. That is far more specific than a restatement of the name, though the verb is implicit (fetch/analyze) rather than stated.

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 mention of 'optional profit from your cost' implicitly tells the agent when to supply cost, and 'on 8 eBay sites' implies the marketplace selector. However there is no explicit when-to-use or when-not-to-use guidance, and no statement about what happens if marketplace is omitted.

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

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

Annotations already declare readOnlyHint and openWorldHint, so the safety profile is covered. The description adds materially by disclosing the paid model — $0.02 per call settled in USDC on Base via x402 — which an agent must know before invoking, plus the shape of returned data. No rate limits or failure modes are described.

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 sentences, front-loaded with what the tool returns and closing with the cost and payment mechanism. Dense but waste-free; the long enumeration of returned fields is the only mild readability cost.

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 read-only search with no output schema, the description covers the return contents, the maximum result count, and the payment prerequisite — the critical unknowns. It lacks any note on result ordering, pagination, or what happens when no listings match.

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% and enums are documented inline, so the schema carries the parameter burden. The description adds only the 'up to 100 listings' ceiling, which restates the schema's max of 100 rather than adding new meaning. Baseline 3 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 verb and resource — live Poshmark US fashion resale listings for a keyword — and enumerates the returned payload (market summary, up to 100 listings with price, brand, size, condition, likes). The parenthetical identifies the marketplace, which implicitly separates it from vinted_search and ebay_market, but no explicit sibling comparison is made.

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 context is implied by 'keyword' search and the named marketplace, and the $0.02 per-call cost gives the agent a reason to be selective. However, there is no explicit guidance on when to choose this over vinted_search or ebay_market, nor any statement of when not to use it.

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

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

Annotations already declare readOnlyHint and openWorldHint, so the bar is lower, and the description still adds the operationally critical detail that each call costs $0.02 in USDC on Base via x402 — a real payment/auth prerequisite an agent must know before invoking. It also discloses the shape of what comes back, though it says nothing about failure modes, rate limits, or empty-result behavior.

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 dense sentences: the payload and its fields come first, the cost model last. No filler, no restating of the tool name, and the parenthetical explaining Reverb earns its place for agents unfamiliar with the marketplace.

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 describing the return contents in detail (median asking price by condition, share taking offers, top makes, cheapest with postage, plus listing fields). For a seven-parameter search tool this is close to complete; only pagination and error/empty-result handling are unaddressed.

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?

With 100% schema description coverage the schema already documents all seven parameters, so the baseline applies. The description adds marginal meaning — 'up to 100 listings' clarifies the max ceiling and 'cheapest with postage' hints at what the shipsTo filter surfaces — but it does not explain how priceMin/priceMax interact with currency or how condition filtering affects the median calculation.

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 ('Live Reverb ... listings for a keyword') and names the marketplace with a parenthetical gloss, which cleanly separates it from the sibling marketplace searches (ebay_market, poshmark_search, vinted_search). It goes further by enumerating both halves of the payload: the market summary and the listing fields.

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 implied rather than prescribed: an agent can infer this is the Reverb-specific marketplace search, and the stated $0.02 cost gives a decision factor, but there is no explicit when-to-use/when-not or a named alternative to route to when the user wants a different marketplace or a non-gear search.

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

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

Annotations only declare readOnlyHint and openWorldHint, so the important additions here are the paid-access model: $0.02 per call, settled in USDC on Base via x402. That is exactly the kind of operational fact an agent needs before invoking and it is not derivable from annotations or schema. It stops short of disclosing rate limits, failure modes when a store is not Shopify, or whether results are cached.

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 sentences, no filler. The catalogue scope is front-loaded and the payment terms are placed last as a gating detail. The enumeration of returned fields earns its space because there is no output schema to carry that information.

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 compensates by enumerating the returned fields, and it discloses the payment mechanism – the two biggest gaps for this tool. Minor omissions remain around pagination beyond the 100 cap and behaviour for invalid or non-Shopify store addresses, but an agent has enough to call it 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 description coverage is 100%, so all four parameters are self-documenting and the baseline is 3. The description reinforces the 100-product ceiling that matches the max parameter, but adds no meaning for keyword or onlyOnSale beyond what the schema already states, and its field list describes outputs rather than inputs.

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 description names a concrete resource (a Shopify store's catalogue) and spells out exactly what comes back: a store summary with price range, share on sale, stock, new-in-30-days and top product types, plus up to 100 products with price, was-price, discount, stock, variants, vendor and date added. It is distinguishable from the marketplace siblings (ebay_market, poshmark_search, vinted_search) by naming Shopify explicitly, though it is framed as a noun phrase rather than a verb+resource action.

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?

There is no when-to-use or when-not-to-use guidance and no routing to a sibling tool for overlapping needs (e.g. keyword search over a single store vs. cross-marketplace search). The only decision-relevant context offered is the price, which helps the agent weigh cost but does not tell it when this tool is the right choice.

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

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

Annotations only declare readOnlyHint and openWorldHint; the description adds materially more — a $0.03 per-call charge paid in USDC on Base via x402 (an auth/payment prerequisite), a 50-listing ceiling per call, and the fact that the resale check is conditional on country. It stops short of describing failure modes, latency, or pagination, so not a 5.

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?

One dense sentence that front-loads the resource and coverage, then stacks returns, conditional feature, limits, and cost in a logical order. It is efficient but the parenthetical field list and the payment clause make it a single long run-on that could be split for scanability.

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 carries the return-value burden and does so by listing the fields shipped, the statistics, and the profit estimate. The remaining gap is the undocumented price-range parameters, which an agent would need to infer from the names alone.

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?

At 67% schema coverage, the description adds real meaning for compareWithEbay (only available for UK, FR, DE, IT, ES) and reinforces keyword scoping as a single term and the 50-item cap on max. However, minPrice and maxPrice have no schema description and no explanation in the description, and the 'price with buyer fee' note is not tied to the range filters.

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 description names a specific resource (Vinted listings) and scope (one keyword, 14 countries) and enumerates the returned fields plus price statistics and an eBay resale/profit check. This is clearly distinct from siblings like poshmark_search and ebay_market without needing to name them.

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 implied by the scope statement and the per-call cost disclosure gives an agent a reason to weigh the call, but there is no explicit when-to-use or when-not-to-use guidance and no pointer to the alternative tools (poshmark_search, ebay_market) for adjacent needs.

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