Anthropic Messages API mock: content blocks and stream failures

Create Message: API overloaded

Documented Synthetic illustrative example from the catalogue, not a live capture. Run only after installing your own receiver. Replace <your-receiver-token> locally; no request is sent from this page.

HTTP 529 · overloaded_error

curl / Bash request

printf '%s' '{"model":"claude-sonnet-5-5","max_tokens":64,"messages":[{"role":"user","content":"Hello"}]}' | \
curl -i -X POST \
  'https://nottherealapi.com/r/<your-receiver-token>/v1/messages' \
  -H 'x-api-key: synthetic-anthropic-key' \
  -H 'anthropic-version: 2023-06-01' \
  -H 'Content-Type: application/json' \
  --data-binary @-

PowerShell request

$body = '{"model":"claude-sonnet-5-5","max_tokens":64,"messages":[{"role":"user","content":"Hello"}]}'
Invoke-WebRequest `
    -UseBasicParsing `
    -Uri 'https://nottherealapi.com/r/<your-receiver-token>/v1/messages' `
    -Method POST `
    -Headers @{
    'x-api-key' = 'synthetic-anthropic-key'
    'anthropic-version' = '2023-06-01'
    } `
    -ContentType 'application/json' `
    -Body ([Text.Encoding]::UTF8.GetBytes($body))

Selected synthetic response

HTTP 529
content-type: application/json

{
  "type": "error",
  "error": {
    "type": "overloaded_error",
    "message": "Overloaded"
  },
  "request_id": "req_example_004"
}

Stream Message: Error after partial output

Documented Synthetic illustrative example from the catalogue, not a live capture. Run only after installing your own receiver. Replace <your-receiver-token> locally; no request is sent from this page.

HTTP 200 · SSE · Stream error after partial output

curl / Bash request

printf '%s' '{"model":"claude-sonnet-5-5","max_tokens":64,"stream":true,"messages":[{"role":"user","content":"Hello"}]}' | \
curl -i --no-buffer -X POST \
  'https://nottherealapi.com/r/<your-receiver-token>/v1/messages' \
  -H 'x-api-key: synthetic-anthropic-key' \
  -H 'anthropic-version: 2023-06-01' \
  -H 'Content-Type: application/json' \
  --data-binary @-

PowerShell request

$body = '{"model":"claude-sonnet-5-5","max_tokens":64,"stream":true,"messages":[{"role":"user","content":"Hello"}]}'
Invoke-WebRequest `
    -UseBasicParsing `
    -Uri 'https://nottherealapi.com/r/<your-receiver-token>/v1/messages' `
    -Method POST `
    -Headers @{
    'x-api-key' = 'synthetic-anthropic-key'
    'anthropic-version' = '2023-06-01'
    } `
    -ContentType 'application/json' `
    -Body ([Text.Encoding]::UTF8.GetBytes($body))

Selected synthetic response

HTTP 200
content-type: text/event-stream; charset=utf-8

event: message_start
data: {"type":"message_start","message":{"id":"msg_example_001","type":"message","role":"assistant","content":[],"model":"claude-sonnet-5-5","stop_reason":null,"stop_sequence":null,"usage":{"input_tokens":12,"output_tokens":0}}}

event: content_block_start
data: {"type":"content_block_start","index":0,"content_block":{"type":"text","text":""}}

event: content_block_delta
data: {"type":"content_block_delta","index":0,"delta":{"type":"text_delta","text":"Partial"}}

event: error
data: {"type":"error","error":{"type":"overloaded_error","message":"Overloaded"}}

Events above are the fixed fixture sequence. Delivery timing is simulated; see the full behaviour list for completion, error and early EOF choices.