Environment and Skills
Run commands on the environment
Not everything needs to go through the agent loop. InvokeAgentRuntimeCommand gives you direct shell access to the harness microVM: deterministic command execution with no model reasoning, no token cost, no ambiguity.
Use it to:
-
Run deterministic pre-invocation or post-invocation scripts.
-
Prepare the environment before an invocation: clone a repo, install dependencies, copy input files.
-
Act on what the agent produced: run tests, commit and push, extract build artifacts.
-
Inspect the VM during development: ls, cat, env, python --version without a round trip through the model.
Example
- AgentCore CLI
-
# Install dependencies before the agent starts
agentcore invoke --exec --harness my-agent --session-id "$(uuidgen)" \
"pip install pandas matplotlib"
# After the agent finishes, inspect what it created
agentcore invoke --exec --harness my-agent --session-id "$(uuidgen)" \
"ls -la /tmp && cat /tmp/results.csv"
The base environment includes Python and bash. For tools like git, node, or other runtimes, install them at session start (e.g. apt-get install -y git) or use a custom environment.
In the TUI, press ! to enter exec mode and run commands inline.
-
AWS CLI/boto3
-
response = client.invoke_agent_runtime_command(
agentRuntimeArn=HARNESS_ARN,
runtimeSessionId=SESSION_ID,
body={"command": "ls -la /workspace"},
)
for event in response["stream"]:
chunk = event.get("chunk", {})
if "contentDelta" in chunk:
delta = chunk["contentDelta"]
if "stdout" in delta:
print(delta["stdout"], end="", flush=True)
if "stderr" in delta:
print(delta["stderr"], end="", flush=True)
elif "contentStop" in chunk:
print(f"\n[exit code: {chunk['contentStop']['exitCode']}]")
See InvokeAgentRuntimeCommand API for details.
Custom environment (container images)
The base environment includes Python and bash, enough for most tasks. When you need more, package your source code, dependencies, runtimes, and tools into a container image, push it to ECR, and reference it on the harness. Your agent runs in that exact environment. Pair custom images with InvokeAgentRuntimeCommand for session-specific setup that varies per invocation.
Container images must be built for the linux/arm64 platform.
The harness overrides your container’s ENTRYPOINT and CMD to keep it running as an environment. Your installed software, filesystem, and environment variables are available to the agent; your container’s startup command is not executed. If you need a background process (such as a dev server), start it via InvokeAgentRuntimeCommand after the session begins.
Example
- AgentCore CLI
-
Scaffold a harness with a Dockerfile:
agentcore create --name coding-agent --container ./Dockerfile
agentcore deploy
At deploy, the CLI builds the image, pushes to ECR, and attaches it to the harness.
Or reference a pre-built image:
agentcore create --name node-agent \
--container public.ecr.aws/docker/library/node:slim
agentcore deploy
-
AWS CLI/boto3
-
aws bedrock-agentcore-control create-harness \
--harness-name "CodingAgent" \
--execution-role-arn "arn:aws:iam::123456789012:role/MyHarnessRole" \
--environment-artifact '{"optionalValue": {"containerConfiguration": {"containerUri": "123456789012.dkr.ecr.us-west-2.amazonaws.com/my-dev-env:latest"}}}' \
--system-prompt '[{"text": "You are an expert TypeScript developer."}]'
The execution role needs ECR pull permissions. See the execution role policy for details.
Environment variables
Set environment variables that are passed to the runtime container. Environment variables are available to the agent and any custom container running in the session.
Example
- AgentCore CLI
-
Set environment variables in harness.json:
{
"environmentVariables": {
"MY_API_URL": "https://api.example.com",
"LOG_LEVEL": "debug"
}
}
Run agentcore deploy to apply.
-
AWS CLI/boto3
-
aws bedrock-agentcore-control create-harness \
--harness-name "MyHarness" \
--execution-role-arn "arn:aws:iam::123456789012:role/MyHarnessRole" \
--environment-variables '{"MY_API_URL": "https://api.example.com", "LOG_LEVEL": "debug"}'
Agent Skills
Agent Skills are bundles of markdown and scripts that give the agent domain knowledge on demand (e.g. how to work with Excel files, how to use a specific API). Skills must be present in the harness environment (the container filesystem) before they can be used. The skills parameter on the harness or at invoke time is a pointer to a path inside the environment — it does not upload or install the skill.
Getting skills into the environment
Bake into the container image — include the skill directory in your custom image at a known path (e.g. .agents/skills/xlsx). Available to all invocations automatically. This is the recommended approach for production.
Install at session start — use InvokeAgentRuntimeCommand to install skills after the session begins, before invoking the agent:
agentcore invoke --exec --harness my-agent --session-id "$(uuidgen)" \
"npx @anthropic-ai/agent-skills add xlsx github"
Pointing the harness at installed skills
Example
- AgentCore CLI
-
Persist skills on the harness:
agentcore add harness --name my-agent \
--skill-path .agents/skills/xlsx \
--skill-path .agents/skills/github
agentcore deploy
Skills configured this way are stored on the harness and passed to every invocation.
Override skills on a single invocation:
agentcore invoke --harness my-agent --skill-path .agents/skills/xlsx \
"Find errors in the Excel files"
-
AWS CLI/boto3
-
Pass skills in the invoke call to override the harness-configured skills for that call only:
response = client.invoke_harness(
harnessArn=HARNESS_ARN,
runtimeSessionId=SESSION_ID,
skills=[{"path": ".agents/skills/xlsx"}],
messages=[{"role": "user", "content": [{"text": "Find errors in the Excel files"}]}],
)
