AWS Lambda

Connect

This Free service needs no license key. Start Vera as in Get started, then run this in a terminal of its own, from an empty scratch directory. It gives the official AWS CLI dummy credentials and a config file of its own, so no AWS account is needed and your own AWS profile isn't touched.

export VERA_ENDPOINT="http://localhost:5003"
export AWS_ACCESS_KEY_ID=test AWS_SECRET_ACCESS_KEY=test
export AWS_REGION=us-east-1 AWS_DEFAULT_REGION=us-east-1
export AWS_SHARED_CREDENTIALS_FILE=/dev/null
export AWS_EC2_METADATA_DISABLED=true
export AWS_PAGER="" AWS_CLI_AUTO_PROMPT=off
unset AWS_PROFILE AWS_DEFAULT_PROFILE
unset AWS_SESSION_TOKEN AWS_SECURITY_TOKEN
unset AWS_WEB_IDENTITY_TOKEN_FILE AWS_ROLE_ARN AWS_ROLE_SESSION_NAME
unset AWS_CONTAINER_CREDENTIALS_FULL_URI
unset AWS_CONTAINER_CREDENTIALS_RELATIVE_URI
cat > vera-aws-config <<'EOF'
[default]
region = us-east-1
output = json
cli_binary_format = base64
s3 =
    addressing_style = path
EOF
export AWS_CONFIG_FILE="$PWD/vera-aws-config"

When you've finished every example in this terminal, close it and delete vera-aws-config, not before.

Use the AWS CLI’s lambda commands. The emulator serves the 2015-03-31 API over the REST JSON protocol, and the examples use us-east-1. That’s the API’s model version: each operation’s path carries a date of its own, such as /2015-03-31/ for functions, /2018-10-31/ for layers and /2014-11-13/ for InvokeAsync, and the coverage notes give every operation’s path.

A new function needs an execution role from the emulator’s IAM. In Vera 1.2.2, function setup worked with a freshly created role. A role ARN that doesn’t exist isn’t a substitute: in Vera 1.2.0 preview, CreateFunction rejected it with ResourceNotFoundException. This page’s example only reads what’s there, so it needs no role.

Example

List the functions, then read the account’s settings. Both only read: the example creates no resources and no local files, so it needs no cleanup.

aws --endpoint-url "$VERA_ENDPOINT" lambda list-functions
aws --endpoint-url "$VERA_ENDPOINT" lambda get-account-settings

On an empty emulator the first command returns no functions:

Output

{ "Functions": [] }

The second returns the account’s settings. These are selected fields. They’re the limits the emulator reports, not evidence that it enforces concurrency:

Output (selected fields)

{
  "AccountLimit": {
    "ConcurrentExecutions": 1000,
    "UnreservedConcurrentExecutions": 1000
  }
}

Supported features

• Function inventory and account settings: ListFunctions and GetAccountSettings, as in the example.
• Function records. In Vera 1.2.2, function setup worked with a freshly created IAM role. In a separate check of Vera 1.2.0 preview, with a role record that already existed in the emulator, CreateFunction succeeded on its fifth attempt (see Limitations). GetFunction read the function back and DeleteFunction deleted it.
• Invocation types and their status codes: a synchronous call answered 200 with the submitted payload, an Event call 202 and a DryRun call 204, the last two with empty bodies. No handler ran.
• Listed in the earlier implementation inventory; not rechecked since: versions and aliases, layers, event source mappings, function URLs, concurrency and provisioned concurrency, code signing, event invoke configs, permissions, durable executions and tags.

Limitations

The main limits are below. A few more apply to every service, and the API coverage notes cover smaller differences.

• Handler code didn’t run. In Vera 1.2.2, invocation echoed its input instead of running the handler. In testing of Vera 1.2.0 preview, synchronous invocation echoed the submitted payload rather than the handler’s result: the package’s Python handler would have returned {"handler_executed": true}, and the response was the payload sent. Event and DryRun calls return only their status codes.
• New functions needed retries in earlier testing. In earlier testing, and in Vera 1.2.0 preview with a role record that already existed, CreateFunction failed four times with InvalidParameterValueException, saying the role couldn’t be assumed, before the fifth call succeeded.
• Not verified beyond those calls: versions, aliases, triggers, function URLs, destinations, timeouts and code execution. Nothing triggered a function or called its URL.

API coverage

Every operation in AWS's published 2015-03-31 API (SDK model, botocore 1.43.105), and whether the emulator implements it. Availability combines the earlier implementation inventory with the dated observations below; checking a page's example does not verify every operation. Each note names its evidence first; an observation given without a build or date comes from earlier testing, on 3 November 2026. What the statuses mean

Operation	Status	Notes
AddLayerVersionPermission	Implemented	Served at POST /2018-10-31/layers/{LayerName}/versions/{VersionNumber}/policy.
AddPermission	Implemented	Served at POST /2015-03-31/functions/{FunctionName}/policy.
CheckpointDurableExecution	Implemented	Served at POST /2025-12-01/durable-executions/{DurableExecutionArn}/checkpoint.
CreateAlias	Implemented	Served at POST /2015-03-31/functions/{FunctionName}/aliases.
CreateCapacityProvider	Implemented	Served at POST /2025-11-30/capacity-providers.
CreateCodeSigningConfig	Implemented	Served at POST /2020-04-22/code-signing-configs.
CreateEventSourceMapping	Implemented	Served at POST /2015-03-31/event-source-mappings.
CreateFunction	Implemented	Served at POST /2015-03-31/functions. Local observation: Vera 1.2.2, 8 November 2026 — function setup worked with a freshly created IAM role. In earlier testing, the first four calls for a new role and function failed with InvalidParameterValueException, saying the role can't be assumed, and the fifth succeeded. Local observation: Vera 1.2.0 preview, 5 November 2026 — the same happened with an IAM role record that already existed, since creating a role failed in that release, and a role ARN that doesn't exist was rejected with ResourceNotFoundException.
CreateFunctionUrlConfig	Implemented	Served at POST /2021-10-31/functions/{FunctionName}/url.
DeleteAlias	Implemented	Served at DELETE /2015-03-31/functions/{FunctionName}/aliases/{Name}.
DeleteCapacityProvider	Implemented	Served at DELETE /2025-11-30/capacity-providers/{CapacityProviderName}.
DeleteCodeSigningConfig	Implemented	Served at DELETE /2020-04-22/code-signing-configs/{CodeSigningConfigArn}.
DeleteEventSourceMapping	Implemented	Served at DELETE /2015-03-31/event-source-mappings/{UUID}.
DeleteFunction	Implemented	Served at DELETE /2015-03-31/functions/{FunctionName}. Local observation: Vera 1.2.0 preview, 5 November 2026 — succeeded for a function created with a role record that already existed.
DeleteFunctionCodeSigningConfig	Implemented	Served at DELETE /2020-06-30/functions/{FunctionName}/code-signing-config.
DeleteFunctionConcurrency	Implemented	Served at DELETE /2017-10-31/functions/{FunctionName}/concurrency.
DeleteFunctionEventInvokeConfig	Implemented	Served at DELETE /2019-09-25/functions/{FunctionName}/event-invoke-config.
DeleteFunctionUrlConfig	Implemented	Served at DELETE /2021-10-31/functions/{FunctionName}/url.
DeleteLayerVersion	Implemented	Served at DELETE /2018-10-31/layers/{LayerName}/versions/{VersionNumber}.
DeleteProvisionedConcurrencyConfig	Implemented	Served at DELETE /2019-09-30/functions/{FunctionName}/provisioned-concurrency.
DeleteResourcePolicy	Not implemented
GetAccountSettings	Implemented	Served at GET /2016-08-19/account-settings. Local observation: Vera 1.2.0 preview, 5 November 2026 — returned the account's reported limits, such as 1000 concurrent executions, in this page's example. Whether they're enforced wasn't checked.
GetAlias	Implemented	Served at GET /2015-03-31/functions/{FunctionName}/aliases/{Name}.
GetCapacityProvider	Implemented	Served at GET /2025-11-30/capacity-providers/{CapacityProviderName}.
GetCodeSigningConfig	Implemented	Served at GET /2020-04-22/code-signing-configs/{CodeSigningConfigArn}.
GetDurableExecution	Implemented	Served at GET /2025-12-01/durable-executions/{DurableExecutionArn}.
GetDurableExecutionHistory	Implemented	Served at GET /2025-12-01/durable-executions/{DurableExecutionArn}/history.
GetDurableExecutionState	Implemented	Served at GET /2025-12-01/durable-executions/{DurableExecutionArn}/state.
GetEventSourceMapping	Implemented	Served at GET /2015-03-31/event-source-mappings/{UUID}.
GetFunction	Implemented	Served at GET /2015-03-31/functions/{FunctionName}. Local observation: Vera 1.2.0 preview, 5 November 2026 — succeeded for a function created with a role record that already existed.
GetFunctionCodeSigningConfig	Implemented	Served at GET /2020-06-30/functions/{FunctionName}/code-signing-config.
GetFunctionConcurrency	Implemented	Served at GET /2019-09-30/functions/{FunctionName}/concurrency.
GetFunctionConfiguration	Implemented	Served at GET /2015-03-31/functions/{FunctionName}/configuration.
GetFunctionEventInvokeConfig	Implemented	Served at GET /2019-09-25/functions/{FunctionName}/event-invoke-config.
GetFunctionRecursionConfig	Implemented	Served at GET /2024-08-31/functions/{FunctionName}/recursion-config.
GetFunctionScalingConfig	Implemented	Served at GET /2025-11-30/functions/{FunctionName}/function-scaling-config.
GetFunctionUrlConfig	Implemented	Served at GET /2021-10-31/functions/{FunctionName}/url.
GetLayerVersion	Implemented	Served at GET /2018-10-31/layers/{LayerName}/versions/{VersionNumber}.
GetLayerVersionByArn	Implemented	Served at GET /2018-10-31/layers?find=LayerVersion.
GetLayerVersionPolicy	Implemented	Served at GET /2018-10-31/layers/{LayerName}/versions/{VersionNumber}/policy.
GetPolicy	Implemented	Served at GET /2015-03-31/functions/{FunctionName}/policy.
GetProvisionedConcurrencyConfig	Implemented	Served at GET /2019-09-30/functions/{FunctionName}/provisioned-concurrency.
GetResourcePolicy	Not implemented
GetRuntimeManagementConfig	Implemented	Served at GET /2021-07-20/functions/{FunctionName}/runtime-management-config.
Invoke	Known difference	Local observation: Vera 1.2.2, 8 November 2026 — invocation echoed its input instead of running the handler. Local observation: Vera 1.2.0 preview, 5 November 2026 — a synchronous call to POST /2015-03-31/functions/{FunctionName}/invocations answered 200 with the submitted payload, not the handler's result. Event calls answered 202 and DryRun calls 204, with empty bodies. No handler code ran.
InvokeAsync	Implemented	Served at POST /2014-11-13/functions/{FunctionName}/invoke-async.
InvokeWithResponseStream	Implemented	Served at POST /2021-11-15/functions/{FunctionName}/response-streaming-invocations.
ListAliases	Implemented	Served at GET /2015-03-31/functions/{FunctionName}/aliases.
ListCapacityProviders	Implemented	Served at GET /2025-11-30/capacity-providers.
ListCodeSigningConfigs	Implemented	Served at GET /2020-04-22/code-signing-configs.
ListDurableExecutionsByFunction	Implemented	Served at GET /2025-12-01/functions/{FunctionName}/durable-executions.
ListEventSourceMappings	Implemented	Served at GET /2015-03-31/event-source-mappings.
ListFunctionEventInvokeConfigs	Implemented	Served at GET /2019-09-25/functions/{FunctionName}/event-invoke-config/list.
ListFunctionUrlConfigs	Implemented	Served at GET /2021-10-31/functions/{FunctionName}/urls.
ListFunctionVersionsByCapacityProvider	Implemented	Served at GET /2025-11-30/capacity-providers/{CapacityProviderName}/function-versions.
ListFunctions	Implemented	Served at GET /2015-03-31/functions. Local observation: Vera 1.2.0 preview, 5 November 2026 — returned an empty Functions list on an empty emulator, in this page's example.
ListFunctionsByCodeSigningConfig	Implemented	Served at GET /2020-04-22/code-signing-configs/{CodeSigningConfigArn}/functions.
ListLayerVersions	Implemented	Served at GET /2018-10-31/layers/{LayerName}/versions.
ListLayers	Implemented	Served at GET /2018-10-31/layers.
ListProvisionedConcurrencyConfigs	Implemented	Served at GET /2019-09-30/functions/{FunctionName}/provisioned-concurrency?List=ALL.
ListTags	Implemented	Served at GET /2017-03-31/tags/{Resource}.
ListVersionsByFunction	Implemented	Served at GET /2015-03-31/functions/{FunctionName}/versions.
PublishLayerVersion	Implemented	Served at POST /2018-10-31/layers/{LayerName}/versions.
PublishVersion	Implemented	Served at POST /2015-03-31/functions/{FunctionName}/versions.
PutFunctionCodeSigningConfig	Implemented	Served at PUT /2020-06-30/functions/{FunctionName}/code-signing-config.
PutFunctionConcurrency	Implemented	Served at PUT /2017-10-31/functions/{FunctionName}/concurrency.
PutFunctionEventInvokeConfig	Implemented	Served at PUT /2019-09-25/functions/{FunctionName}/event-invoke-config.
PutFunctionRecursionConfig	Implemented	Served at PUT /2024-08-31/functions/{FunctionName}/recursion-config.
PutFunctionScalingConfig	Implemented	Served at PUT /2025-11-30/functions/{FunctionName}/function-scaling-config.
PutProvisionedConcurrencyConfig	Implemented	Served at PUT /2019-09-30/functions/{FunctionName}/provisioned-concurrency.
PutResourcePolicy	Not implemented
PutRuntimeManagementConfig	Implemented	Served at PUT /2021-07-20/functions/{FunctionName}/runtime-management-config.
RemoveLayerVersionPermission	Implemented	Served at DELETE /2018-10-31/layers/{LayerName}/versions/{VersionNumber}/policy/{StatementId}.
RemovePermission	Implemented	Served at DELETE /2015-03-31/functions/{FunctionName}/policy/{StatementId}.
SendDurableExecutionCallbackFailure	Implemented	Served at POST /2025-12-01/durable-execution-callbacks/{CallbackId}/fail.
SendDurableExecutionCallbackHeartbeat	Implemented	Served at POST /2025-12-01/durable-execution-callbacks/{CallbackId}/heartbeat.
SendDurableExecutionCallbackSuccess	Implemented	Served at POST /2025-12-01/durable-execution-callbacks/{CallbackId}/succeed.
StopDurableExecution	Implemented	Served at POST /2025-12-01/durable-executions/{DurableExecutionArn}/stop.
TagResource	Implemented	Served at POST /2017-03-31/tags/{Resource}.
UntagResource	Implemented	Served at DELETE /2017-03-31/tags/{Resource}.
UpdateAlias	Implemented	Served at PUT /2015-03-31/functions/{FunctionName}/aliases/{Name}.
UpdateCapacityProvider	Implemented	Served at PUT /2025-11-30/capacity-providers/{CapacityProviderName}.
UpdateCodeSigningConfig	Implemented	Served at PUT /2020-04-22/code-signing-configs/{CodeSigningConfigArn}.
UpdateEventSourceMapping	Implemented	Served at PUT /2015-03-31/event-source-mappings/{UUID}.
UpdateFunctionCode	Implemented	Served at PUT /2015-03-31/functions/{FunctionName}/code.
UpdateFunctionConfiguration	Implemented	Served at PUT /2015-03-31/functions/{FunctionName}/configuration.
UpdateFunctionEventInvokeConfig	Implemented	Served at POST /2019-09-25/functions/{FunctionName}/event-invoke-config.
UpdateFunctionUrlConfig	Implemented	Served at PUT /2021-10-31/functions/{FunctionName}/url.