> ## Documentation Index
> Fetch the complete documentation index at: https://docs.lithoblocks.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Limits and validation

> Find enforced text, block, payload, rate, and subscription limits.

Limits apply to the compiled output, so a short template can exceed them after expanding an array or substituting long text.

## Read the current contract

`GET /v1/templates/block-schema` returns `limits`, supported block types, directive operators, and `interactivity.limits`. Use it as the current reference for text lengths, chart dimensions, card actions, carousel size, and metadata size.

| Boundary                            | Current documented limit                                                                                                                                                     |
| ----------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| Slack message                       | 50 compiled blocks                                                                                                                                                           |
| Modal view                          | 100 compiled blocks                                                                                                                                                          |
| Modal title and submit/close labels | 24 characters                                                                                                                                                                |
| Interactive message metadata        | 3,800 bytes for action configuration and original send context together; space is reserved within Slack’s 4,000-byte total metadata limit for the wrapper and log references |
| Bulk-send destinations              | 1–100 per request                                                                                                                                                            |
| Queue-ingest events                 | Up to 100 per request                                                                                                                                                        |
| Destination timeout                 | 1,000–60,000 ms; default 10,000 ms                                                                                                                                           |
| Authoring requests                  | 120 per minute per organization; a 429 includes `Retry-After`                                                                                                                |

The endpoint schema is authoritative for request size, field limits, and pagination. Subscription limits for active queues, modes, and event volume depend on the organization; inspect `tier_limit` errors and account settings rather than assuming a published plan table is current.

## Validate realistic extremes

1. Read the selected template's input schema.
2. Test longest expected text, empty arrays, and maximum expected row counts.
3. Run `POST /v1/templates/validate` with the complete blocks and representative `sample_data`.
4. Inspect the generated output and measured interactivity metadata.
5. Send to a test channel and check the actual Slack rendering.

Limit arrays before sending, split large reports, and link to the full source when the message should be a summary. A successful local validation does not establish that every future input will fit.

[Directives](/guides/templates-directives) · [Tables](/guides/templates-table-blocks) · [Troubleshooting](/guides/troubleshooting)