Menu
Amazon Lex
Developer Guide

Limits

This section describes current limits in Amazon Lex. These limits are grouped by categories.

General Limits

Currently, Amazon Lex is available in us-east-1 region.

Service Region Name Region Endpoint Protocol
Model building service US East (N. Virginia) us-east-1 models.lex.us-east-1.amazonaws.com HTTPS
Runtime service US East (N. Virginia) us-east-1 runtime.lex.us-east-1.amazonaws.com HTTPS

Currently, Amazon Lex supports only US English language. That is, Amazon Lex trains your bots to understand only US English.

Runtime Service Limits

Currently, Amazon Lex is available in us-east-1 region.

Region Name Region Endpoint Protocol
US East (N. Virginia) us-east-1 runtime.lex.us-east-1.amazonaws.com HTTPS

In addition to the limits described in the API reference, note the following:

  • API

    • Input speech in the PostContent can be up to 15 seconds long.

       

    • In both the runtime API operations PostContent and PostText, the input text size can be up to 1024 Unicode characters.

       

    • The total header size of a PostContent header is 16 KB. The total size of the session attributes in a PostContent request and response is 12 KB.

       

    • The maximum input size to a Lambda function is 12 KB. The maximum output size is 25 KB, of which 12 KB can be session attributes.

       

Model Building Limits

Model building refers to creating and managing bots. This includes creating and managing bots, intents, slot types, slots, and bot channel associations.

Currently, Amazon Lex is available in us-east-1 region.

Region Name Region Endpoint Protocol
US East (N. Virginia) us-east-1 models.lex.us-east-1.amazonaws.com HTTPS

Bot Limits

  • You configure prompts and statements throughout the model building API. Each of these prompts or statements can have up to five messages and each message can contain from 1 to 1000 UTF-8 characters.

     

  • You can define sample utterances for intents and slots. You can use a maximum of 200,000 characters for all utterances.

     

  • Bot, alias, and bot channel association names are case insensitive at the time of creation. If you create PizzaBot and then try to create pizzaBot, you will get an error. However, when accessing a resource, the resource names are case sensitive, you must specify PizzaBot and not pizzaBot. These names must be between 2 and 50 ASCII characters.

     

  • The maximum number of versions you can publish for all resource types is 100. Note that there is no versioning for aliases.

     

  • Within a bot, intent names and slot names must be unique, you can't have an intent and a slot by the same name.

     

  • You can create a bot that is configured to support multiple intents. If two intents have a slot by the same name, then the corresponding slot type must be the same.

     

    For example, suppose you create a bot to support two intents (OrderPizza and OrderDrink). If both these intents have the size slot, then the slot type must be the same in both places.

     

    In addition, the sample utterances you provide for a slot in one of the intents applies to a slot with the same name in other intents.

     

  • You can associate a maximum of 100 intents with a bot.

     

  • When you create a bot, you specify a session timeout. The session timeout can be between one minute and one day. The default is five minutes.

     

    This timeout determines how long the bot can retain conversation context, such as current user intent and slot data.

     

    In addition, note that after a user starts the conversation with your bot and until the session expires, Amazon Lex uses the same bot version (even if you update the bot alias to point to another version).

     

  • When you update the $LATEST version of the bot, Amazon Lex terminates any in-progress conversations for any client application using the $LATEST version of the bot). Generally, you should not use the $LATEST version of a bot in production because $LATEST version can be updated. You should publish a version and use it instead.

     

  • When you update an alias, Amazon Lex takes a few minutes to pick up the change. When you modify the $LATEST version of the bot, the change is picked up immediately.

     

  • The $LATEST version of your bot should only be used for manual testing while building the bot. Amazon Lex limits the number of runtime requests that you can make to the $LATEST version of the bot.

     

  • You can create up to five aliases for a bot.

     

  • You can create up to 100 bots per AWS account.

     

  • You cannot create multiple intents that extend from the same built-in intent.

     

Intent Limits

  • Intent and slot names are case insensitive at the time of creation. That is, if you create OrderPizza intent and then again try to create another orderPizza intent, you will get an error. However, when accessing these resources, the resource names are case sensitive, specify OrderPizza and not orderPizza. These names must be between 1 and 100 ASCII characters.

     

  • An intent can have up to 1,500 sample utterances. A minimum of one sample utterance is required. Each sample utterance can be up to 200 UTF-8 characters long. You can use up to 200,000 characters for all intent and slot utterances in a bot. A sample utterance for an intent:

    • Can refer to zero or more slot names.

    • Can refer to a slot name only once.

    For example:

    Copy
    I want a pizza I want a {pizzaSize} pizza I want a {pizzaSize} {pizzaTopping} pizza

     

  • Although each intent supports up to 1,500 utterances, if you use fewer utterances Amazon Lex may have a better ability to recognize inputs outside your provided set.

     

  • Each slot can have up to 10 sample utterances. Each sample utterance must refer to the slot name exactly once. For example:

    Copy
    {pizzaSize} please

     

  • Each bot can have a maximum of 200,000 characters for intent and slot utterences combined.

     

  • You cannot provide utterances for intents that extend from built-in intents. For all other intents you must provide at least one sample utterance. Intents contain slots, but the slot level sample utterances are optional.

     

  • Built-in intents

    • Currently, Amazon Lex does not support slot elicitation for built-in intents. You cannot create Lambda functions to return the ElicitSlot directive in the response with an intent that is derived from built-in intents. For more information, see Response Format.

    • The service does not support adding sample utterances to built-in intents. Similarly, you cannot add or remove slots to built-in intents.

     

  • You can create up to 1,000 intents per AWS account. You can create up to 100 slots in an intent.

     

Slot Type Limits

  • Slot type names are case insensitive at the time of creation. If you create the PizzaSize slot type and then again try to create the pizzaSize slot type, you will get an error. However, when accessing these resources, the resource names are case sensitive (you must specify PizzaSize and not pizzaSize). These names must be between 1 and 100 ASCII characters.

     

  • Resource (bot, intent, alias, slot, slot type) names are case insensitive.

     

    A custom slot type you create can have a maximum of 10,000 enumeration values, and each enumeration value can be up to 140 UTF-8 characters long. The enumeration values cannot contain duplicates.

     

  • For a slot type value, where appropriate, specify both upper and lower case. For example, for a slot type called Procedure, if value is MRI, specify both MRI and mri as values.

     

  • Built-in slot types – Currently, Amazon Lex doesn't support adding enumeration values for the built-in slot types.