Short answer: the look to book ratio (L2B) is the number of search or availability requests you send a supplier for every booking you make through them. A ratio of 500:1 means five hundred searches per booking. Suppliers police it because each search costs them compute while only bookings earn revenue, so partners with runaway ratios face throttling, fees or disconnection. Metasearch, price calendars, bots and AI shopping agents all push the ratio up; caching, throttling and smarter search bring it back down.
What look to book actually measures
A "look" is any request that makes the supplier do pricing work: an availability check, a fare search, a shopping request. A "book" is a completed reservation. Divide one by the other over a period and you have the partner's look to book ratio - effectively the travel industry's version of a conversion rate, seen from the supplier's side of the API. Industry commentary such as Travel in Motion's analysis of NDC shopping traffic frames it exactly this way: shopping requests versus actual bookings.
The ratio has climbed for years. When booking meant phoning an agent, a handful of looks preceded each sale. Web search made looking free for consumers; metasearch made it free across dozens of sellers at once; and automated shopping keeps multiplying it. The supplier's cost per search, however, never became free.
Why suppliers police it
Pricing an itinerary is real work: fares, rules, availability and taxes have to be evaluated per request, whether by an airline's own systems, a GDS shopping farm or a bed bank's availability layer. Bookings pay for that infrastructure; searches only consume it. A partner sending millions of searches and few bookings is, from the supplier's perspective, a cost centre degrading performance for everyone else - Travelport's own API best-practice documentation, for example, pushes integrators toward workflows that reduce unnecessary availability calls.
The pressure has sharpened recently because automated agents do not get tired and do not stop at good enough. Amadeus has publicly positioned precomputed fare products as a response to AI-driven shopping traffic that breaks the assumptions traditional systems were sized for. Expect policing to get stricter, not looser.
What pushes the ratio up
- Metasearch by design. A metasearch user compares many providers per query and books with at most one, so every party in the chain sees more looks per book. This is inherent to the model - see how flight metasearch engines work.
- Price calendars and flexible-date views. One screen of "cheapest day to fly" represents dozens of route-date queries.
- Bots and scrapers. Competitor price monitoring and content scraping generate looks that can never convert.
- AI shopping agents. Automated planners iterate through options at machine speed, multiplying search volume without adding bookings proportionally.
- Sloppy integration. Re-searching on every pagination click, failing to reuse recent results, or polling suppliers for idle background refreshes all inflate the ratio for no user benefit.
How limits show up in contracts
Suppliers rarely publish hard numbers, and the specifics vary by supplier, product and negotiation, but the mechanisms are consistent:
| Mechanism | How it works |
|---|---|
| Contractual L2B targets | The agreement names an expected ratio band; sustained breaches trigger review. Industry sources describe tolerated ratios ranging from tens to hundreds of searches per booking depending on the channel. |
| Per-search or excess fees | Searches beyond an included allowance are billed, converting your inefficiency into supplier revenue. |
| Technical throttling | Rate limits per second or per day cap what you can send regardless of contract terms. |
| Degraded service | Heavy shoppers may be shifted to cached or lower-priority availability rather than full live pricing. |
| Suspension | Persistent abuse, especially bot-like traffic, ends with credentials being revoked. |
The practical takeaway: ask every supplier what their expectations are before you integrate, and design your architecture around the tightest answer. This is a standard discovery question in our flight API integration and hotel API integration projects.
How engines keep the ratio down
Almost everything that controls L2B is a variation on one idea: answer as many looks as possible without asking the supplier.
- Caching. Recent results serve repeat and adjacent queries; calendars and route pages run on precomputed estimates. This is the single biggest lever, covered in depth in our guide to flight fare caching strategies.
- Bot filtering. Scraper and crawler traffic is identified and served from cache or blocked, so it never touches supplier quota.
- Smart search routing. Not every query needs every supplier: engines learn which sources actually win on which routes and skip the rest, cutting fan-out per search.
- Debouncing and session reuse. Pagination, sorting and small parameter tweaks reuse the session's result set instead of re-shopping.
- Quota budgeting. Per-supplier budgets throttle background refresh first and user-facing search last, so contractual limits are never breached by warm-up traffic.
Why L2B shapes API pricing
Supplier pricing models are, underneath, look to book management by other means. Free or cheap search paired with booking-based revenue only works for the supplier if ratios stay sane, so allowances, tiers and excess-search fees exist to keep them there. Channels built for high-ratio traffic - metasearch feeds and cached shopping products - are priced and engineered differently from booking channels, which is why the same supplier can quote very different terms for what sounds like the same data.
For anyone building a flight aggregator website or a meta flight website, the lesson is to treat searches as a metered resource from day one. Sites that spend quota deliberately - cached where users browse, live where users buy - get better terms, better performance and fewer awkward supplier conversations than sites that discover L2B when the first warning email arrives.
This article is general information about travel technology and online marketing. It is not legal, tax or financial advice, and advertising platform policies change often. Check the current policy documents and take professional advice for your own situation.