diff --git a/README.md b/README.md
index eac9afa..b75206e 100644
--- a/README.md
+++ b/README.md
@@ -31,6 +31,10 @@ agent config list                 # list saved agent configs
 agent config get <config-id>      # show one config as YAML (-o json for JSON)
 agent config init [path]          # scaffold a starter config (default: agents/my_agent.yaml)
 
+agent sandbox variable list       # list sandbox env variable names (values are write-only)
+agent sandbox variable set A=1 B=2     # create/update variables (or --from-file .env/.json)
+agent sandbox variable rm K       # delete a variable
+
 agent budget                      # current budget summary
 agent usage                       # usage dashboard for the period
 agent ping                        # check authenticated /v1 connectivity
diff --git a/src/cli.tsx b/src/cli.tsx
index 27c66ed..59f4729 100644
--- a/src/cli.tsx
+++ b/src/cli.tsx
@@ -3,6 +3,7 @@ import { registerLogin } from './commands/login'
 import { registerMe } from './commands/me'
 import { registerRun } from './commands/run'
 import { registerConfig } from './commands/config'
+import { registerSandbox } from './commands/sandbox'
 import { registerTemplate } from './commands/template'
 import { registerUsage } from './commands/usage'
 import { registerPing } from './commands/ping'
@@ -19,6 +20,7 @@ registerLogin(program)
 registerMe(program)
 registerRun(program)
 registerConfig(program)
+registerSandbox(program)
 registerTemplate(program)
 registerUsage(program)
 registerPing(program)
diff --git a/src/commands/sandbox.ts b/src/commands/sandbox.ts
new file mode 100644
index 0000000..61921ad
--- /dev/null
+++ b/src/commands/sandbox.ts
@@ -0,0 +1,160 @@
+import { type Command } from 'commander'
+import { readFileSync } from 'node:fs'
+import { ApiClient } from '../lib/api'
+import { formatTs, printJson, printTable, runAction } from '../lib/output'
+import type { SandboxVariableInput, SandboxVariableSummary } from '../lib/types'
+
+export function registerSandbox(program: Command): void {
+  const sandbox = program.command('sandbox').description('Manage sandbox resources')
+
+  const variable = sandbox
+    .command('variable')
+    .alias('var')
+    .description('Manage sandbox environment variables (values are write-only)')
+
+  variable
+    .command('list')
+    .alias('ls')
+    .description('List sandbox environment variables (GET /v1/sandboxes/variables)')
+    .option('--json', 'output raw JSON')
+    .action(async (opts: { json?: boolean }) => {
+      await runAction(async () => {
+        const variables = await new ApiClient().listSandboxVariables()
+        printVariables(variables, opts.json)
+      })
+    })
+
+  variable
+    .command('set [assignments...]')
+    .description('Create or update variables, e.g. `set A=1 B=2` (PUT /v1/sandboxes/variables)')
+    .option('-f, --from-file <path>', 'load variables from a .env or .json file')
+    .option('--json', 'output raw JSON')
+    .action(async (assignments: string[], opts: { fromFile?: string; json?: boolean }) => {
+      await runAction(async () => {
+        const inputs = collectInputs(assignments, opts.fromFile)
+        const variables = await new ApiClient().putSandboxVariables(inputs)
+        if (!opts.json) {
+          const names = inputs.map((v) => v.name).join(', ')
+          console.log(`✓ stored ${inputs.length} variable(s) (values hidden): ${names}`)
+        }
+        printVariables(variables, opts.json)
+      })
+    })
+
+  variable
+    .command('rm <name>')
+    .alias('delete')
+    .description('Delete a variable (DELETE /v1/sandboxes/variables/{name})')
+    .option('--json', 'output raw JSON')
+    .action(async (name: string, opts: { json?: boolean }) => {
+      await runAction(async () => {
+        const variables = await new ApiClient().deleteSandboxVariable(name)
+        if (!opts.json) console.log(`✓ deleted ${name}`)
+        printVariables(variables, opts.json)
+      })
+    })
+}
+
+// Build the upsert batch from inline `KEY=VALUE` arguments and/or a file. File
+// pairs come first so an inline arg with the same name overrides the file (the
+// server upserts in order, last write wins). Name validation is left to the
+// server (one source of truth for the rules); we only parse and require that
+// the caller gave us something to send.
+export function collectInputs(
+  assignments: string[],
+  fromFile: string | undefined,
+): SandboxVariableInput[] {
+  const inputs: SandboxVariableInput[] = []
+  if (fromFile) {
+    const fileInputs = readVarsFromFile(fromFile)
+    if (fileInputs.length === 0) throw new Error(`no variables found in ${fromFile}`)
+    inputs.push(...fileInputs)
+  }
+  for (const raw of assignments) {
+    const parsed = parseAssignment(raw)
+    if (parsed === null) {
+      throw new Error(`invalid assignment '${raw}' (expected KEY=VALUE)`)
+    }
+    inputs.push(parsed)
+  }
+  if (inputs.length === 0) {
+    throw new Error('provide KEY=VALUE pairs, or --from-file <path>')
+  }
+  return inputs
+}
+
+// Read a variables file, picking the format by extension: `.json` is a flat
+// object of name → value, anything else is a .env-style KEY=VALUE file.
+function readVarsFromFile(path: string): SandboxVariableInput[] {
+  const contents = readFileSync(path, 'utf8')
+  return path.toLowerCase().endsWith('.json')
+    ? parseJsonVars(contents)
+    : parseEnvFile(contents)
+}
+
+// Parse a flat JSON object of name → value. Values must be strings (sandbox
+// variable values are strings); a nested object, array, or non-string value is
+// rejected rather than silently coerced.
+export function parseJsonVars(contents: string): SandboxVariableInput[] {
+  let parsed: unknown
+  try {
+    parsed = JSON.parse(contents)
+  } catch (err) {
+    throw new Error(`invalid JSON: ${(err as Error).message}`)
+  }
+  if (parsed === null || typeof parsed !== 'object' || Array.isArray(parsed)) {
+    throw new Error('expected a JSON object of variable name to value')
+  }
+  const inputs: SandboxVariableInput[] = []
+  for (const [name, value] of Object.entries(parsed)) {
+    if (typeof value !== 'string') {
+      throw new Error(`value for '${name}' must be a string`)
+    }
+    inputs.push({ name, value })
+  }
+  return inputs
+}
+
+// Parse one `KEY=VALUE` assignment. Strips an optional leading `export `, splits
+// on the first `=` (so values may contain `=`), and removes matching surrounding
+// quotes. Returns null when there is no `=`.
+export function parseAssignment(raw: string): SandboxVariableInput | null {
+  const line = raw.trim()
+  const withoutExport = line.startsWith('export ') ? line.slice(7).trim() : line
+  const eq = withoutExport.indexOf('=')
+  if (eq === -1) return null
+  const name = withoutExport.slice(0, eq).trim()
+  let value = withoutExport.slice(eq + 1).trim()
+  if (value.length >= 2 && (value[0] === '"' || value[0] === "'") && value.at(-1) === value[0]) {
+    value = value.slice(1, -1)
+  }
+  return { name, value }
+}
+
+// Parse a .env-style file: one `KEY=VALUE` per line, with blank lines and `#`
+// comments skipped. Each non-comment line is parsed by parseAssignment.
+export function parseEnvFile(contents: string): SandboxVariableInput[] {
+  const inputs: SandboxVariableInput[] = []
+  for (const raw of contents.split('\n')) {
+    const line = raw.trim()
+    if (line === '' || line.startsWith('#')) continue
+    const parsed = parseAssignment(line)
+    if (parsed !== null) inputs.push(parsed)
+  }
+  return inputs
+}
+
+function printVariables(variables: SandboxVariableSummary[], json?: boolean): void {
+  if (json) {
+    printJson(variables)
+    return
+  }
+  if (variables.length === 0) {
+    console.log('No sandbox variables.')
+    return
+  }
+  printTable(
+    ['NAME', 'CREATED', 'UPDATED'],
+    variables.map((v) => [v.name, formatTs(v.created_at), formatTs(v.updated_at)]),
+  )
+}
diff --git a/src/lib/api.ts b/src/lib/api.ts
index 06805ed..4b527b1 100644
--- a/src/lib/api.ts
+++ b/src/lib/api.ts
@@ -7,10 +7,13 @@ import type {
   CliAuthStart,
   CreateAgentConfigRequest,
   CreatedAgentConfig,
+  GetSandboxVariablesResponse,
   ListAgentConfigsResponse,
   ListAgentRunsQuery,
   ListAgentRunsResponse,
   ListAgentTemplatesResponse,
+  SandboxVariableInput,
+  SandboxVariableSummary,
   SavedAgentConfig,
   StartAgentRunRequest,
   UsageDashboard,
@@ -124,6 +127,37 @@ export class ApiClient {
     return this.request('GET', `/v1/agents/configs/${encodeURIComponent(configId)}`)
   }
 
+  // -------------------------- sandbox variables ---------------------------
+  // All three return the full current list (the backend echoes it after every
+  // mutation), so callers can render the resulting state.
+
+  async listSandboxVariables(): Promise<SandboxVariableSummary[]> {
+    const res = await this.request<GetSandboxVariablesResponse>(
+      'GET',
+      '/v1/sandboxes/variables',
+    )
+    return res.variables
+  }
+
+  async putSandboxVariables(
+    variables: SandboxVariableInput[],
+  ): Promise<SandboxVariableSummary[]> {
+    const res = await this.request<GetSandboxVariablesResponse>(
+      'PUT',
+      '/v1/sandboxes/variables',
+      { variables },
+    )
+    return res.variables
+  }
+
+  async deleteSandboxVariable(name: string): Promise<SandboxVariableSummary[]> {
+    const res = await this.request<GetSandboxVariablesResponse>(
+      'DELETE',
+      `/v1/sandboxes/variables/${encodeURIComponent(name)}`,
+    )
+    return res.variables
+  }
+
   // ---------------------------- agent templates ---------------------------
 
   async listAgentTemplates(): Promise<AgentTemplate[]> {
diff --git a/src/lib/types.ts b/src/lib/types.ts
index 9bcfcde..fd2a58d 100644
--- a/src/lib/types.ts
+++ b/src/lib/types.ts
@@ -178,6 +178,30 @@ export interface ListAgentRunsQuery {
   limit?: number
 }
 
+// -------------------------- sandbox variables ---------------------------
+// Customer-scoped environment variables injected into a sandbox when an agent
+// config names them. Values are write-only: the API accepts them but never
+// returns them, so the summary carries only the name and timestamps.
+
+export interface SandboxVariableSummary {
+  name: string
+  created_at: string
+  updated_at: string
+}
+
+export interface GetSandboxVariablesResponse {
+  variables: SandboxVariableSummary[]
+}
+
+export interface SandboxVariableInput {
+  name: string
+  value: string
+}
+
+export interface PutSandboxVariablesRequest {
+  variables: SandboxVariableInput[]
+}
+
 // ------------------------------ cli auth --------------------------------
 
 export interface CliAuthStart {
diff --git a/test/api.test.ts b/test/api.test.ts
index b5bd09a..a148e75 100644
--- a/test/api.test.ts
+++ b/test/api.test.ts
@@ -93,6 +93,52 @@ describe('ApiClient.request', () => {
   })
 })
 
+describe('ApiClient sandbox variables', () => {
+  afterEach(() => vi.unstubAllGlobals())
+
+  it('lists variables and unwraps the response envelope', async () => {
+    const fetchMock = vi.fn(
+      async () =>
+        new Response(JSON.stringify({ variables: [{ name: 'A', created_at: '', updated_at: '' }] }), {
+          status: 200,
+        }),
+    )
+    vi.stubGlobal('fetch', fetchMock)
+
+    const out = await new ApiClient('http://api.test', 't').listSandboxVariables()
+    expect(out).toEqual([{ name: 'A', created_at: '', updated_at: '' }])
+    expect(fetchMock.mock.calls[0][0]).toBe('http://api.test/v1/sandboxes/variables')
+    expect((fetchMock.mock.calls[0][1] as RequestInit).method).toBe('GET')
+  })
+
+  it('PUTs the variables batch and returns the echoed list', async () => {
+    const fetchMock = vi.fn(
+      async () => new Response(JSON.stringify({ variables: [] }), { status: 200 }),
+    )
+    vi.stubGlobal('fetch', fetchMock)
+
+    await new ApiClient('http://api.test', 't').putSandboxVariables([{ name: 'TOKEN', value: 'x' }])
+    const [url, init] = fetchMock.mock.calls[0]
+    expect(url).toBe('http://api.test/v1/sandboxes/variables')
+    expect((init as RequestInit).method).toBe('PUT')
+    expect(JSON.parse((init as RequestInit).body as string)).toEqual({
+      variables: [{ name: 'TOKEN', value: 'x' }],
+    })
+  })
+
+  it('URL-encodes the name on delete', async () => {
+    const fetchMock = vi.fn(
+      async () => new Response(JSON.stringify({ variables: [] }), { status: 200 }),
+    )
+    vi.stubGlobal('fetch', fetchMock)
+
+    await new ApiClient('http://api.test', 't').deleteSandboxVariable('MY/VAR')
+    const [url, init] = fetchMock.mock.calls[0]
+    expect(url).toBe('http://api.test/v1/sandboxes/variables/MY%2FVAR')
+    expect((init as RequestInit).method).toBe('DELETE')
+  })
+})
+
 describe('agent templates', () => {
   afterEach(() => vi.unstubAllGlobals())
 
diff --git a/test/sandbox.test.ts b/test/sandbox.test.ts
new file mode 100644
index 0000000..265852a
--- /dev/null
+++ b/test/sandbox.test.ts
@@ -0,0 +1,106 @@
+import { describe, expect, it } from 'vitest'
+import {
+  collectInputs,
+  parseAssignment,
+  parseEnvFile,
+  parseJsonVars,
+} from '../src/commands/sandbox'
+
+describe('parseJsonVars', () => {
+  it('parses a flat object of name → value', () => {
+    expect(parseJsonVars('{"A":"1","B":"two"}')).toEqual([
+      { name: 'A', value: '1' },
+      { name: 'B', value: 'two' },
+    ])
+  })
+
+  it('accepts an empty object', () => {
+    expect(parseJsonVars('{}')).toEqual([])
+  })
+
+  it('throws on invalid JSON', () => {
+    expect(() => parseJsonVars('{not json}')).toThrow(/invalid JSON/)
+  })
+
+  it('rejects a top-level array', () => {
+    expect(() => parseJsonVars('["A","B"]')).toThrow(/object of variable name/)
+  })
+
+  it('rejects non-string values', () => {
+    expect(() => parseJsonVars('{"A":1}')).toThrow(/value for 'A' must be a string/)
+    expect(() => parseJsonVars('{"A":{"nested":"x"}}')).toThrow(/value for 'A' must be a string/)
+  })
+})
+
+describe('parseAssignment', () => {
+  it('parses KEY=VALUE', () => {
+    expect(parseAssignment('A=1')).toEqual({ name: 'A', value: '1' })
+  })
+
+  it('splits on the first = so values may contain =', () => {
+    expect(parseAssignment('URL=https://x.test/?a=b')).toEqual({
+      name: 'URL',
+      value: 'https://x.test/?a=b',
+    })
+  })
+
+  it('strips a leading `export ` and surrounding quotes', () => {
+    expect(parseAssignment('export TOKEN="abc"')).toEqual({ name: 'TOKEN', value: 'abc' })
+  })
+
+  it('returns null when there is no =', () => {
+    expect(parseAssignment('NOEQUALS')).toBeNull()
+  })
+})
+
+describe('collectInputs', () => {
+  it('collects multiple inline assignments', () => {
+    expect(collectInputs(['A=1', 'B=2'], undefined)).toEqual([
+      { name: 'A', value: '1' },
+      { name: 'B', value: '2' },
+    ])
+  })
+
+  it('throws on an inline arg with no =', () => {
+    expect(() => collectInputs(['A=1', 'BAD'], undefined)).toThrow(/invalid assignment 'BAD'/)
+  })
+
+  it('throws when given nothing', () => {
+    expect(() => collectInputs([], undefined)).toThrow(/provide KEY=VALUE/)
+  })
+})
+
+describe('parseEnvFile', () => {
+  it('parses KEY=VALUE pairs', () => {
+    expect(parseEnvFile('A=1\nB=two')).toEqual([
+      { name: 'A', value: '1' },
+      { name: 'B', value: 'two' },
+    ])
+  })
+
+  it('skips blank lines and # comments', () => {
+    expect(parseEnvFile('\n# a comment\nA=1\n\n')).toEqual([{ name: 'A', value: '1' }])
+  })
+
+  it('strips a leading `export `', () => {
+    expect(parseEnvFile('export TOKEN=abc')).toEqual([{ name: 'TOKEN', value: 'abc' }])
+  })
+
+  it('splits on the first = so values may contain =', () => {
+    expect(parseEnvFile('URL=https://x.test/?a=b')).toEqual([
+      { name: 'URL', value: 'https://x.test/?a=b' },
+    ])
+  })
+
+  it('strips matching surrounding quotes', () => {
+    expect(parseEnvFile(`A="quoted"\nB='single'\nC="mismatch'`)).toEqual([
+      { name: 'A', value: 'quoted' },
+      { name: 'B', value: 'single' },
+      { name: 'C', value: `"mismatch'` },
+    ])
+  })
+
+  it('ignores lines with no =', () => {
+    expect(parseEnvFile('NOEQUALS\nA=1')).toEqual([{ name: 'A', value: '1' }])
+  })
+})